intel/i945: Use define for `BSM`

Change-Id: Ia58d8b410a145f27f0b267c115714580c366e063
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/5929
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)
1 file changed