dt-bindings: net: mediatek,net: Correct bindings for MT7981

dt-bindings: net: mediatek,net: Correct bindings for MT7981

Different SoCs have different numbers of Wireless Ethernet
Dispatch (WED) units:
- MT7981: Has 1 WED unit
- MT7986: Has 2 WED units
- MT7988: Has 2 WED units

Update the binding to reflect these hardware differences. The MT7981
also uses infracfg for PHY switching, so allow that property.

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251115-openwrt-one-network-v4-6-48cbda2969ac@collabora.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>