wifi: rtw89: add skeleton of mac80211 chanctx ops support

Support mac80211 chanctx series ops. Still, currently support
single channel. Based on this premise, things should be similar
to before. So, we haven't dealt with relationship between vif
and chanctx in depth. Instead, we leave both ::assign_vif()
and ::unassign_vif() as noops for now.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220809104952.61355-12-pkshih@realtek.com