ath10k: provision to support periodic peer stats update

Enable support for periodic peer stats update when peer stats
service is enabled. The host to update the peer stats received
from the firmware periodically, since firmware will reset this to zero
after sometime (due to memory constraints)

While enabling periodic peer / vdev stats cleanup the existing
list in debugfs if max limit is reached, so that the new stats is
updated.

Ideally speaking based on 'Michal Kazior's' suggestion
we need to completely move to periodic update of all the stats making
the 'ping - pong' method obselete. This requires a bit of re-work and
some testing as well, also confirmation regarding backward comptability
for various firmware and chipsets. Hence allow periodic update only
for peer_stats.

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>