mt76: introduce mcu_reset function pointer in mt76_mcu_ops structure

Introduce mcu_reset function pointer in mt76_mcu_ops structure in order
to run hw related reset function for the mcu running on the chipset.
This is a preliminary patch to introduce chip reset for mt7921 devices.

Co-developed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>