ath10k: limit multi-vif ps more aggresivelly

Further testing proved that multi-channel AP+STA
on QCA6174 with RM.2.0-00088 should have powersave
force-disabled to avoid beacon misses/skipping on
either side which in turn could disrupt
communication.

Since AP never has arvif->ps don't even bother
checking it. Other combinations may be broken as
well so disallow powersave with multivif outright
unless firmware advertises otherwise.

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