[][mt7981: Enable i2c in kernel]

[Description]
Add mt7981 compatible
Fix I2C dts file

[Release-log]
N/A

Change-Id: I3466d328f40578e45dbe300011b20c4689132342
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5394285
3 files changed