dt-bindings: net: rockchip-dwmac: add rk3308 gmac compatible

The Rockchip RK3308 has a gmac that is not fully compatible with any of the
other Rockchip gmacs.
This patch adds a compatible string for it.
Signed-off-by: Tobias Schramm <t.schramm@manjaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/rockchip-dwmac.yaml

@@ -19,6 +19,7 @@ select:
           - rockchip,rk3128-gmac
           - rockchip,rk3228-gmac
           - rockchip,rk3288-gmac
+          - rockchip,rk3308-gmac
           - rockchip,rk3328-gmac
           - rockchip,rk3366-gmac
           - rockchip,rk3368-gmac
@@ -38,6 +39,7 @@ properties:
           - rockchip,rk3128-gmac
           - rockchip,rk3228-gmac
           - rockchip,rk3288-gmac
+          - rockchip,rk3308-gmac
           - rockchip,rk3328-gmac
           - rockchip,rk3366-gmac
           - rockchip,rk3368-gmac