mt76: mt7615: introduce set_bmc and st_sta for uni commands

Introduce mt7615_mcu_uni_set_bmc and mt7615_mcu_uni_set_sta routines for
mt7663e commands.

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>