dt-bindings: timer: Add CLINT bindings

We add DT bindings documentation for CLINT device.
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Tested-by: Emil Renner Berhing <kernel@esmil.dk>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Documentation/devicetree/bindings/timer/sifive,clint.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/timer/sifive,clint.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: SiFive Core Local Interruptor
+
+maintainers:
+  - Palmer Dabbelt <palmer@dabbelt.com>
+  - Anup Patel <anup.patel@wdc.com>
+
+description:
+  SiFive (and other RISC-V) SOCs include an implementation of the SiFive
+  Core Local Interruptor (CLINT) for M-mode timer and M-mode inter-processor
+  interrupts. It directly connects to the timer and inter-processor interrupt
+  lines of various HARTs (or CPUs) so RISC-V per-HART (or per-CPU) local
+  interrupt controller is the parent interrupt controller for CLINT device.
+  The clock frequency of CLINT is specified via "timebase-frequency" DT
+  property of "/cpus" DT node. The "timebase-frequency" DT property is
+  described in Documentation/devicetree/bindings/riscv/cpus.yaml
+
+properties:
+  compatible:
+    items:
+      - const: sifive,fu540-c000-clint
+      - const: sifive,clint0
+
+    description:
+      Should be "sifive,<chip>-clint" and "sifive,clint<version>".
+      Supported compatible strings are -
+      "sifive,fu540-c000-clint" for the SiFive CLINT v0 as integrated
+      onto the SiFive FU540 chip, and "sifive,clint0" for the SiFive
+      CLINT v0 IP block with no chip integration tweaks.
+      Please refer to sifive-blocks-ip-versioning.txt for details
+
+  reg:
+    maxItems: 1
+
+  interrupts-extended:
+    minItems: 1
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - interrupts-extended
+
+examples:
+  - |
+    timer@2000000 {
+      compatible = "sifive,fu540-c000-clint", "sifive,clint0";
+      interrupts-extended = <&cpu1intc 3 &cpu1intc 7
+                             &cpu2intc 3 &cpu2intc 7
+                             &cpu3intc 3 &cpu3intc 7
+                             &cpu4intc 3 &cpu4intc 7>;
+       reg = <0x2000000 0x10000>;
+    };
+...