thermal/drivers/mtk: Add support for MT7986 and MT7981

Add support for V3 generation thermal found in MT7986 and MT7981 SoCs.
Brings code to assign values from efuse as well as new function to
convert raw temperature to millidegree celsius, as found in MediaTek's
SDK sources (but cleaned up and de-duplicated)

[1]: https://git01.mediatek.com/plugins/gitiles/openwrt/feeds/mtk-openwrt-feeds/+/baf36c7eef477aae1f8f2653b6c29e2caf48475b



Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/2d341fc45266217249586eb4bd3be3ac4ca83a12.1674055882.git.daniel@makrotopia.org


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>