x86, cpu, amd: Fix crash as Xen Dom0 on AMD Trinity systems

f7f286a9 ("x86/amd: Re-enable CPU topology extensions in case BIOS
has disabled it") wrongfully added code which used the AMD-specific
{rd,wr}msr variants for no real reason.

This caused boot panics on xen which wasn't initializing the
{rd,wr}msr_safe_regs pv_ops members properly.

This, in turn, caused a heated discussion leading to us reviewing all
uses of the AMD-specific variants and removing them where unneeded
(almost everywhere except an obscure K8 BIOS fix, see 6b0f43dd).

Finally, this patch switches to the standard {rd,wr}msr*_safe* variants
which should've been used in the first place anyway and avoided unneeded
excitation with xen.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Link: http://lkml.kernel.org/r/1338562358-28182-4-git-send-email-bp@amd64.org
Cc: Andreas Herrmann <andreas.herrmann3@amd.com>
Link: <http://lkml.kernel.org/r/1338383402-3838-1-git-send-email-andre.przywara@amd.com

>
[Boris: correct and expand commit message]
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>