dt-bindings: timer: add Andes machine timer

Add the DT binding documentation for Andes machine timer.

The RISC-V architecture defines a machine timer that provides a real-time
counter and generates timer interrupts. Andes machiner timer (PLMT0) is
the implementation of the machine timer, and it contains memory-mapped
registers (mtime and mtimecmp). This device supports up to 32 cores.

Acked-by: Conor Dooley <[e-mail]>
Signed-off-by: Ben Zong-You Xie <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnd Bergmann <[e-mail]>

Documentation/devicetree/bindings/timer/andestech,plmt0.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/timer/andestech,plmt0.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Andes machine-level timer
+
+description:
+  The Andes machine-level timer device (PLMT0) provides machine-level timer
+  functionality for a set of HARTs on a RISC-V platform. It has a single
+  fixed-frequency monotonic time counter (MTIME) register and a time compare
+  register (MTIMECMP) for each HART connected to the PLMT0. A timer interrupt is
+  generated if MTIME >= MTIMECMP.
+
+maintainers:
+  - Ben Zong-You Xie <[e-mail]>
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - andestech,qilai-plmt
+      - const: andestech,plmt0
+
+  reg:
+    maxItems: 1
+
+  interrupts-extended:
+    minItems: 1
+    maxItems: 32
+    description:
+      Specifies which harts are connected to the PLMT0. Each item must points
+      to a riscv,cpu-intc node, which has a riscv cpu node as parent. The
+      PLMT0 supports 1 hart up to 32 harts.
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - interrupts-extended
+
+examples:
+  - |
+    interrupt-controller@100000 {
+      compatible = "andestech,qilai-plmt", "andestech,plmt0";
+      reg = <0x100000 0x100000>;
+      interrupts-extended = <&cpu0intc 7>,
+                            <&cpu1intc 7>,
+                            <&cpu2intc 7>,
+                            <&cpu3intc 7>;
+    };