ath10k: implement channel switching

Until now channel change wasn't propagating to FW
directly because operational channel is abstracted
by VDEVs and it wasn't really necessary since
ath10k implements hwscan and hwroc.

This effectively fixes STA CSA and allows for
future AP-like CSA as well.

kvalo: change error handling in ath10k_bss_info_changed()

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>