[][Refactor and refine mt7981 eth driver]

[Description]
Refactor and refine mt7981 eth driver

[Release-log]
N/A

Change-Id: I0728f85f82afde3181ff7f4804c3be2c1fa7fae7
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5284163
1 file changed