wifi: rtw89: add flag check for power state

Use POWER_ON flag to make sure power on/off is symmetric. Since both
remain_on_channel and hw_scan both alter the power state, this makes
sure that we don't enter/leave IPS mode twice.
Also, replace IPS related functions with inline function that does
similar logic so we can track it more easily.

Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230411124832.14965-5-pkshih@realtek.com