mwifiex: add set_cqm_rssi_config handler support

In this handler LOW_RSSI and HIGH_RSSI events are subscribed
to FW using provided threshold value so that FW will monitor
connection quality and trigger any of these events.

Driver will notify cfg80211 about connection quality based on
inputs from FW and provided hysteresis.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>