b43: Implement dynamic PHY API

This patch implements a dynamic "ops" based PHY API.
This is needed in order to conveniently support future PHY types
to avoid the "switch"-hell.

This patch does not change any functionality. It just moves lots
of code from one place to another and adjusts it for the changed
data structures.

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