x86, cpu: Preset default tlb_flushall_shift on AMD

Run the mprotect.c microbenchmark on all our families >= K8 and preset
the flushall shift variable accordingly.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Link: http://lkml.kernel.org/r/1344272439-29080-5-git-send-email-bp@amd64.org


Signed-off-by: H. Peter Anvin <hpa@zytor.com>