wl1271: Add proper WLAN-BT co-ex configuration, and enable co-ex.

Add configuration values for the varous WLAN-BT co-ex configuration parameters,
and finally enable WLAN-BT co-ex. Based on preliminary measurements, it
appears the co-ex feature is not increasing WLAN power consumption, if BT
is not activated.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>