[][kernel][mt7988][eth][Refactor path for internal 2.5G phy]

[Description]
Refactor path for internal 2.5G phy.

If without this patch, driver cannot handle the gmii path and
10/100mbps half duplex mode properly.

[Release-log]
N/A


Change-Id: I1d4f372590ee62256f6d33ce4b30a522a37129c9
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6721575
14 files changed