mt76: connac: add 6GHz support to mt76_connac_mcu_sta_tlv

Introduce sta_rec_he_6g_capa tlv in order configure the mcu with 6GHz
capabilities. This is a preliminary patch to enable 6GHz band for
mt7921 devices.

Tested-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>