b43/ssb: Add SPROM8 extraction and LP-PHY detection

This adds detection code for the LP-PHY and SPROM
extraction code for version 8, which is needed by the LP-PHY and
newer N-PHY.

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