dt-bindings: net: sophgo,sg2044-dwmac: add phy mode restriction

dt-bindings: net: sophgo,sg2044-dwmac: add phy mode restriction

As the ethernet controller of SG2044 and SG2042 only supports
RGMII phy. Add phy-mode property to restrict the value.

Also, since SG2042 has internal rx delay in its mac, make
only "rgmii-txid" and "rgmii-id" valid for phy-mode.

Fixes: e281c48a7336 ("dt-bindings: net: sophgo,sg2044-dwmac: Add support for Sophgo SG2042 dwmac")
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251114003805.494387-2-inochiama@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>