dt-bindings: riscv: microchip: add polarberry compatible string

Add a binding for the Sundance Polarberry board.
Acked-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: NConor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220509142610.128590-8-conor.dooley@microchip.comSigned-off-by: NPalmer Dabbelt <palmer@rivosinc.com>

Documentation/devicetree/bindings/riscv/microchip.yaml

@@ -21,6 +21,7 @@ properties:
       - enum:
           - microchip,mpfs-icicle-kit
           - microchip,mpfs-icicle-reference-rtlv2203
+          - sundance,polarberry
       - const: microchip,mpfs
 
 additionalProperties: true