ath10k: add debugfs support to get power save state change of STA

ath10k: add debugfs support to get power save state change of STA

This patch helps to get the power save state change of each peer
connected to the AP. With WMI_10_4_PEER_STA_PS_STATECHG_EVENTID
event, ps state of each peer is reported to user space via
debugfs.

Use the below command to get the ps state of each sta:
cat /sys/kernel/debug/ieee80211/phyX/netdev::wlanX/stations/
XX:XX:XX:XX:XX:XX/peer_ps_state

If STA is in power save state, we get the peer_ps_state value as 1.
if STA is not in power save state, we get the peer_ps_state value as 0.
If ps_state event is disabled, we get the peer_ps_state value as 2.

We can enable/disable the ps_state events using the debugfs flag
"ps_state_enable"

echo Y > /sys/kernel/debug/ieee80211/phyX/ath10k/ps_state_enable

Y = 1 to enable and Y = 0 to disable

Tested in QCA4019 with firmware ver 10.4-3.2.1.1-00011

Signed-off-by: Maharaja Kennadyrajan <mkenna@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>