wl1271: Cleaned up wlan power on/off functions

wl1271: Cleaned up wlan power on/off functions

Added method for wlan power control to io_ops struct and moved
wl1271_power_on and wl1271_power_off functions to wl1271_io.h.

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