Add support to configure quiet period (in milliseconds) via debugfs.
This is useful to experiment different quiet period values along with
different throttle ratio.

echo 100 > /sys/kernel/debug/ieee80211/phyX/ath10k/quiet_period
Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>