ath10k: enable debugfs provision to enable Peer Stats feature

Provide a debugfs entry to enable/ disable Peer Stats feature.
Peer Stats feature is for developers/users who are more interested
in studying in Rx/Tx stats with multiple clients connected, hence
disable this by default. Enabling this feature by default results
in unneccessary processing of Peer Stats event for every 500ms
and updating peer_stats list (allocating memory) and cleaning it up
ifexceeds the higher limit and this can be an unnecessary overhead
during long run stress testing.

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