This path enables AMD OSVW (OS Visible Workaround) feature for Xen. New 
AMD errata will have a OSVW id assigned in the future. OS is supposed to 
check OSVW status MSR to find out whether CPU has a specific erratum. 
Legacy errata are also supported in this patch: traditional 
family/model/stepping approach will be used if OSVW feature isn't 
applicable.  This patch is adapted from Hans Rosenfeld's patch submitted 
to Linux kernel .

Signed-off-by: Wei Huang <wei.huang2@amd.com>
Signed-off-by: Hans Rosenfeld <hands.rosenfeld@amd.com>
Acked-by: Jan Beulich <jbeulich@novell.com>