mt76: mt7615: add more uni mcu commands

Introduce mt7615_mcu_uni_set_bss, mt7615_mcu_uni_set_dev and
mt7615_mcu_uni_set_beacon_offload uni mcu commands. This is a
preliminary patch to add mt7663e support

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