dt-bindings: chosen: remove old .txt binding

chosen.txt has been replaced by a schema in dtschema[1] and is now out
of date as well. Remove it to avoid confusion.

[1] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/chosen.yaml

Link: https://lore.kernel.org/lkml/c8dddfe6-6385-ed34-e789-9f845c8a32bd@linaro.org/
Link: https://lore.kernel.org/lkml/CAL_Jsq+uSdk9YNbUW35yjN3q8-3FDobrxHmBpy=4RKmCfnB0KQ@mail.gmail.com/Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
[robh: Improve commmit msg]
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220628153354.870543-1-Jason@zx2c4.com

Documentation/devicetree/bindings/chosen.txt

-The chosen node
----------------
-
-The chosen node does not represent a real device, but serves as a place
-for passing data between firmware and the operating system, like boot
-arguments. Data in the chosen node does not represent the hardware.
-
-The following properties are recognized:
-
-
-kaslr-seed
------------
-
-This property is used when booting with CONFIG_RANDOMIZE_BASE as the
-entropy used to randomize the kernel image base address location. Since
-it is used directly, this value is intended only for KASLR, and should
-not be used for other purposes (as it may leak information about KASLR
-offsets). It is parsed as a u64 value, e.g.
-
-/ {
-	chosen {
-		kaslr-seed = <0xfeedbeef 0xc0def00d>;
-	};
-};
-
-Note that if this property is set from UEFI (or a bootloader in EFI
-mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by
-the Linux EFI stub (which will populate the property itself, using
-EFI_RNG_PROTOCOL).
-
-stdout-path
------------
-
-Device trees may specify the device to be used for boot console output
-with a stdout-path property under /chosen, as described in the Devicetree
-Specification, e.g.
-
-/ {
-	chosen {
-		stdout-path = "/serial@f00:115200";
-	};
-
-	serial@f00 {
-		compatible = "vendor,some-uart";
-		reg = <0xf00 0x10>;
-	};
-};
-
-If the character ":" is present in the value, this terminates the path.
-The meaning of any characters following the ":" is device-specific, and
-must be specified in the relevant binding documentation.
-
-For UART devices, the preferred binding is a string in the form:
-
-	<baud>{<parity>{<bits>{<flow>}}}
-
-where
-
-	baud	- baud rate in decimal
-	parity	- 'n' (none), 'o', (odd) or 'e' (even)
-	bits	- number of data bits
-	flow	- 'r' (rts)
-
-For example: 115200n8r
-
-Implementation note: Linux will look for the property "linux,stdout-path" or
-on PowerPC "stdout" if "stdout-path" is not found.  However, the
-"linux,stdout-path" and "stdout" properties are deprecated. New platforms
-should only use the "stdout-path" property.
-
-linux,booted-from-kexec
------------------------
-
-This property is set (currently only on PowerPC, and only needed on
-book3e) by some versions of kexec-tools to tell the new kernel that it
-is being booted by kexec, as the booting environment may differ (e.g.
-a different secondary CPU release mechanism)
-
-linux,usable-memory-range
--------------------------
-
-This property holds a base address and size, describing a limited region in
-which memory may be considered available for use by the kernel. Memory outside
-of this range is not available for use.
-
-This property describes a limitation: memory within this range is only
-valid when also described through another mechanism that the kernel
-would otherwise use to determine available memory (e.g. memory nodes
-or the EFI memory map). Valid memory may be sparse within the range.
-e.g.
-
-/ {
-	chosen {
-		linux,usable-memory-range = <0x9 0xf0000000 0x0 0x10000000>;
-	};
-};
-
-The main usage is for crash dump kernel to identify its own usable
-memory and exclude, at its boot time, any other memory areas that are
-part of the panicked kernel's memory.
-
-While this property does not represent a real hardware, the address
-and the size are expressed in #address-cells and #size-cells,
-respectively, of the root node.
-
-linux,elfcorehdr
-----------------
-
-This property holds the memory range, the address and the size, of the elf
-core header which mainly describes the panicked kernel's memory layout as
-PT_LOAD segments of elf format.
-e.g.
-
-/ {
-	chosen {
-		linux,elfcorehdr = <0x9 0xfffff000 0x0 0x800>;
-	};
-};
-
-While this property does not represent a real hardware, the address
-and the size are expressed in #address-cells and #size-cells,
-respectively, of the root node.
-
-linux,initrd-start and linux,initrd-end
----------------------------------------
-
-These properties hold the physical start and end address of an initrd that's
-loaded by the bootloader. Note that linux,initrd-start is inclusive, but
-linux,initrd-end is exclusive.
-e.g.
-
-/ {
-	chosen {
-		linux,initrd-start = <0x82000000>;
-		linux,initrd-end = <0x82800000>;
-	};
-};