[][Add upstream thermal driver for MT7981]

Add upstream thermal driver for MT7981.
Currently the driver supports cross-platform thermal feature.
	- V1 : MT8173, MT8183, MT2701, MT2712
	- V2 : MT7622
	- V3 : MT7981, MT7986

If without this change, MT7981 ASIC is unable to read
ARM CPU temperature.

The way to show current temperature.
	- cat /sys/class/thermal/thermal_zone0/temp


Change-Id: I0244bbb897fffc2f33b494ec4a8f69787a14a6e9
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5401091
3 files changed