[][kernel][mt7988][eth][Refactor USXGMII reset sequence]

[Description]
Refactor USXGMII reset sequence.

If without this patch, SGMII might be reset as well when resetting USXGMII.

[Release-log]
N/A


Change-Id: I7bef3a542b06c2beb339f117fc27a40cacac3bf0
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7267722
2 files changed