[][kernel][common][eth][Add phylink_pcs support for the SGMII/USXGMII]

[Description]
Add phylink_pcs support for the SGMII/USXGMII.

If without this patch, phylink framework cannot configure MAC and PCS
properly for the inband mode.

[Release-log]
N/A


Change-Id: I6cda355eeb2abb3c90a9120f3b77b3721200dc81
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7353960
6 files changed