[][kernel][mt7988][eth][Correct phy-mode for the USXGMII]

[Description]
Change DTS phy-mode to USXGMII instead of 10GKR except for SFP+.

According to the PHY specification, DE suggests chaning phy-mode
to USXGMII which connects with external 10G PHY.

[Release-log]
N/A


Change-Id: Ic51df5d1ee6ecf1ef572b28f3551a3450481e0ed
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7289672
19 files changed