mt76: mt7615: introduce mt7663u support

Introduce support for mt7663u 802.11ac 2x2:2 chipset to mt7615 driver.
Main difference respect to pcie code base is the usb code needs to
configure wtbl from non-atomic context

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>