ath10k: add debugfs support for Per STA total rx duration

Add debugfs support for per client total rx duration, track this
via the report of Peer stats rx duration reported for every 500ms

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