mt76: add headroom and tailroom to mt76_mcu_ops data structure

Introduce headroom and tailroom to mt76_mcu_ops data structure in order
to unify the routine used for mcu message allocation. This is a
preliminary patch to add mt7663u support

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

mt76: add driver for MT7603E and MT7628/7688

This driver is for a newer generation of 2x2 MediaTek 802.11n chipsets.
MT7603E is a PCIe chip.
MT7628 and MT7688 are MIPS SoC devices with built-in WLAN.
MT7688 is limited to 1x1

This driver fully supports AP, station, mesh, ad-hoc and monitor mode.

Signed-off-by: Felix Fietkau <nbd@nbd.name>