b43legacy: Use input-polldev for the rfkill switch

This removes the direct call to rfkill on an rfkill event
and replaces it with an input device. This way userspace is also
notified about the event.

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

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