dt-bindings: riscv: add sophgo sg2042 bindings

Add DT binding documentation for the SOPHGO's SG2042 Soc [1] and the
Milk-V Pioneer board [2].

Link: https://en.sophgo.com/product/introduce/sg2042.html [1]
Link: https://milkv.io/pioneer [2]
Acked-by: Chao Wei <chao.wei@sophgo.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Documentation/devicetree/bindings/riscv/sophgo.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/riscv/sophgo.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sophgo SoC-based boards
+
+maintainers:
+  - Chao Wei <chao.wei@sophgo.com>
+  - Chen Wang <unicorn_wang@outlook.com>
+
+description:
+  Sophgo SoC-based boards
+
+properties:
+  $nodename:
+    const: '/'
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - milkv,pioneer
+          - const: sophgo,sg2042
+
+additionalProperties: true
+
+...

MAINTAINERS

@@ -20063,6 +20063,12 @@ F:	drivers/char/sonypi.c
 F:	drivers/platform/x86/sony-laptop.c
 F:	include/linux/sony-laptop.h
 
+SOPHGO DEVICETREES
+M:	Chao Wei <chao.wei@sophgo.com>
+M:	Chen Wang <unicorn_wang@outlook.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/riscv/sophgo.yaml
+
 SOUND
 M:	Jaroslav Kysela <perex@perex.cz>
 M:	Takashi Iwai <tiwai@suse.com>