p54: implement rfkill

This patch implements a basic rfkill support for p54 hardware and
removes a rfkill related WARNING:

fwio.c: In function ‘p54_setup_mac’:
fwio.c:323: warning: ‘radio_enabled’ is deprecated.

by abandoning radio_enable in flavour for IEEE80211_CONF_CHANGE_IDLE.

Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>