b43: PHY: allow init optimizations by tracking PHY state

PHY has to be often re-initialized (e.g. during band switching after PHY
reset), however some operations have to be performed only once (only
power reset affects them).

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>