mt76: connac: add mt76_connac_mcu_get_nic_capability utility routine

Introduce mt76_connac_mcu_get_nic_capability utility routine to poll
device capabilities returned by mcu fw for CE devices (mt7663/mt7921).
This is a preliminary patch to introduce 6GHz support.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>