mt76: mt7915: add HE bss_conf support for interfaces

Add basic HE BSS's info for interfaces. As for the advanced features
will be added gradually in the future patches.
(i.e. BSS color, TWT, spatial reuse and OFDMA)

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Tested-by: Shayne Chen <shayne.chen@mediatek.com>
Tested-by: Chih-Min Chen <chih-min.chen@mediatek.com>
Tested-by: Evelyn Tsai <evelyn.tsai@mediatek.com>
Acked-by: Yiwei Chung <yiwei.chung@mediatek.com>
Acked-by: YF Luo <yf.luo@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>