b43: Add LP PHY Analog Switch Support

The current verison of b43 uses "b43_phyop_switch_analog_generic" for A,
G and LP phys.

According to the spec, this is the wrong behaviour for the LP PHY
(see: http://bcm-v4.sipsolutions.net/802.11/PHY/Anacore

 )

While no problems on the x86 plattform where seen, this leads to a crash
on the BCM5354 SoC (MIPS 32 LE plattform).
This patch implements the analog switch for LP PHYs according to the
specs. It fixes the crash

signed-off-by: Thomas Ilnseher <illth@gmx.de>

Signed-off-by: John W. Linville <linville@tuxdriver.com>