b43legacy: RF-kill support

This adds full support for the RFKILL button and the RFKILL LED trigger.

This is a port to b43legacy of a patch by Michael Buesch <mb@bu3sch.de>
for b43.

Signed-off-by: Larry <Finger&lt;Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>