[LINUXBIOS] Add the CPU_OPT flag to facilitate passing flags into the build

[LINUXBIOS] Add the CPU_OPT flag to facilitate passing flags into the build

buildROM passes build flags through the CPU_OPT environment variable -
especially -fno-stack-protector for those of us lucky enough to have
Debian/Ubuntu.  This adds  to the cache_as_ram_auto.inc target
for the GA-2761GXDK so that the resulting cpu0.S is clean.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
Acked-by: Ronald G. Minnich <rminnich@gmail.com>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@2911 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1