mt76: mt7915e: Enable thermal management by default

By default, mt7915e does not enable thermal management until the default
thermal zone does not reach a trip point.  If the rest of the system
have better cooling than the wireless hardware, then it is possible that
the wireless chip can overheat while the rest of the system is fine.

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Signed-off-by: Felix Fietkau <nbd@nbd.name>