dt-bindings: arm: Remove obsolete RTSM DCSCB binding

The Arm VExpress DCSCB binding is unused and was only ever used on a s/w
model over 10 years ago. Remove it.
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240510123238.3904779-2-robh@kernel.orgSigned-off-by: Sudeep Holla <sudeep.holla@arm.com>

Documentation/devicetree/bindings/arm/rtsm-dcscb.txt

-ARM Dual Cluster System Configuration Block
--------------------------------------------
-
-The Dual Cluster System Configuration Block (DCSCB) provides basic
-functionality for controlling clocks, resets and configuration pins in
-the Dual Cluster System implemented by the Real-Time System Model (RTSM).
-
-Required properties:
-
-- compatible : should be "arm,rtsm,dcscb"
-
-- reg : physical base address and the size of the registers window
-
-Example:
-
-	dcscb@60000000 {
-		compatible = "arm,rtsm,dcscb";
-		reg = <0x60000000 0x1000>;
-	};