ssb: Update for Rev. 5 SPROM

Although a revision 5 SPROM has not been seen in the wild, the
open-source portion of the MIPS driver 4.150.10.5 describes its
layout, which is mostly inherited from revision 4. This patch
implements the differences.

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