dt-bindings: arm: rockchip: Add Firefly Station M2

The Station M2 is a compact single board computer based on the rk3566
SoC. It outputs on uart2 for debug and console purposes.

Signed-off-by: Peter Geis <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Heiko Stuebner <[e-mail]>

Documentation/devicetree/bindings/arm/rockchip.yaml

···
               - firefly,roc-rk3399-pc-plus
           - const: rockchip,rk3399
 
+      - description: Firefly Station M2
+        items:
+          - const: firefly,rk3566-roc-pc
+          - const: rockchip,rk3566
+
       - description: FriendlyElec NanoPi R2S
         items:
           - const: friendlyarm,nanopi-r2s