F15h, models 0x30 and later don't have a GART. Note that. Also check
CPUID leaf 0x80000006 for L3 prescence because there are models which
don't sport an L3 cache.
Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
[ Boris: rewrite commit message, cleanup comments. ]
Signed-off-by: Borislav Petkov <bp@suse.de>