wifi: mt76: mt7996: add thermal sensor device support

wifi: mt76: mt7996: add thermal sensor device support

This patch adds support for thermal sensor device, including the
following features:
- Support to read current chip temperature.
- Support to set/get the trigger/restore temperature for thermal service.
- Support to read current chip tx cycle.

Signed-off-by: Howard Hsu <howard-yh.hsu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>