b43: Move remaining code from phy.c to phy_a.c

This moves the remaining code from phy.c to phy_a.c
phy.c is removed.
No functional change. Just moving code and removing dead code.

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