[][Add mt7981 eth driver support]

[Description]
Add mt7981 eth driver support
1. sync code from patches-5.4
9100-eth-mtk-add-mt7981.patch
9101-eth-mtk-enable-hw-vlan-offlaod-netsys-v2.patch
9102-eth-mt7981-add-gmac2-gphy-support.patch
9103-eth-mt7981-add-gmac2-sgmii-cophy-support.patch

[Release-log]
N/A

Change-Id: I3af58eee51528c3174142ae1ad2a7cf99ed976a7
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4799707
3 files changed