dt-bindings: arm: rockchip: add Forlinx FET3588-C

FET3588-C is an System on Module made by Forlinx based on Rockchip RK3588.
This SoM used by OK3588-C Board.

FET3588-C features:
- Rockchip RK3588
- LPDDR4 4/8 GB
- eMMC 32/64 GB

Add devicetree binding for Forlinx FET3588-C SoM.
Signed-off-by: Dmitry Yashin <dmt.yashin@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240403151229.30577-2-dmt.yashin@gmail.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -198,6 +198,13 @@ properties:
           - const: firefly,rk3568-roc-pc
           - const: rockchip,rk3568
 
+      - description: Forlinx FET3588-C SoM
+        items:
+          - enum:
+              - forlinx,ok3588-c
+          - const: forlinx,fet3588-c
+          - const: rockchip,rk3588
+
       - description: FriendlyElec NanoPi R2 series boards
         items:
           - enum: