ath10k: setup maximum number of supported stations

Setup maximum number of associated stations supported in
AP/P2P_GO mode.

This allow hostapd/wpa_supplicant to play with that limit
and set more information (eg. P2P group limit bit for P2P_GO).

Signed-off-by: Janusz Dziedzic <janusz.dziedzic@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>