b43: Rewrite suspend/resume code

This removes most of the b43 suspend/resume code (it's handled by mac80211)
and moves the registration of devices to the attachment phase. This is
required, because we must not register/unregister devices on suspend/resume.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>