dt-bindings: riscv: add SpacemiT K1 bindings

Add DT binding documentation for the SpacemiT K1 SoC[1] and the Banana
Pi BPi-F3 board[2] which used it.

Link: https://www.spacemit.com/en/spacemit-key-stone-2/ [1]
Link: https://docs.banana-pi.org/en/BPI-F3/BananaPi_BPI-F3 [2]
Signed-off-by: Yangyu Chen <cyy@cyyself.name>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Matthias Brugger <matthias.bgg@kernel.org>
Signed-off-by: Yixun Lan <dlan@gentoo.org>

Documentation/devicetree/bindings/riscv/spacemit.yaml

@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/riscv/spacemit.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: SpacemiT SoC-based boards
+
+maintainers:
+  - Yangyu Chen <cyy@cyyself.name>
+  - Yixun Lan <dlan@gentoo.org>
+
+description:
+  SpacemiT SoC-based boards
+
+properties:
+  $nodename:
+    const: '/'
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - bananapi,bpi-f3
+          - const: spacemit,k1
+
+additionalProperties: true
+
+...