rtlwifi: Use mutex to replace spin_lock to protect IPS and LPS

Enter/leavel IPS and LPS are large critical section, and they can't use
sleep function because running in atomic-context, which own a spin_lock.
In commit ba9f93f82a ("rtlwifi: Fix enter/exit power_save"), it moves
LPS functions to thread-context, so this commit can simply change LPS's
spin lock to mutex.
Considering IPS functions, rtl_ips_nic_on() may be called by TX tasklet
(softirq-context) that check whether packet is auth frame. Fortunately,
current mac80211 will ask driver to leave IPS using op_config with
changed flag IEEE80211_CONF_CHANGE_IDLE, before issuing auth frame, so
IPS functions can run in thread-context and use mutex to protect critical
section, too.
Also, this commit removes some useless spin locks.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/realtek/rtlwifi/usb.c

@@ -962,7 +962,6 @@ static void _rtl_usb_tx_preprocess(struct ieee80211_hw *hw,
 	memset(&tcb_desc, 0, sizeof(struct rtl_tcb_desc));
 	if (ieee80211_is_auth(fc)) {
 		RT_TRACE(rtlpriv, COMP_SEND, DBG_DMESG, "MAC80211_LINKING\n");
-		rtl_ips_nic_on(hw);
 	}
 
 	if (rtlpriv->psc.sw_ps_enabled) {