dt-bindings: net: snps,dwmac: add missing DWMAC IP version

Add missing DWMAC IP version in snps,dwmac.yaml which found by below
command, as NXP i.MX8 families support SNPS DWMAC 5.10a IP.

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- dt_binding_check DT_SCHEMA_FILES=Documentation/devicetree/bindings/net/nxp,dwmac-imx.yaml
Documentation/devicetree/bindings/net/nxp,dwmac-imx.example.dt.yaml:
ethernet@30bf0000: compatible: None of ['nxp,imx8mp-dwmac-eqos', 'snps,dwmac-5.10a'] are valid under the given schema
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/snps,dwmac.yaml

@@ -28,6 +28,7 @@ select:
           - snps,dwmac-4.00
           - snps,dwmac-4.10a
           - snps,dwmac-4.20a
+          - snps,dwmac-5.10a
           - snps,dwxgmac
           - snps,dwxgmac-2.10
 
@@ -82,6 +83,7 @@ properties:
         - snps,dwmac-4.00
         - snps,dwmac-4.10a
         - snps,dwmac-4.20a
+        - snps,dwmac-5.10a
         - snps,dwxgmac
         - snps,dwxgmac-2.10
 
@@ -375,6 +377,7 @@ allOf:
               - snps,dwmac-4.00
               - snps,dwmac-4.10a
               - snps,dwmac-4.20a
+              - snps,dwmac-5.10a
               - snps,dwxgmac
               - snps,dwxgmac-2.10
               - st,spear600-gmac