b43: Add more N-PHY stuff

This adds some minor stuff for N-PHY support. Nothing special.
Adds Analog switching and some TODOs for RSSI processing.
Just a patch I had floating around for quite some time now.

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