svm: amend c/s 24990:322300fd2ebd (fake BU_CFG MSR on AMD revF)

Let's restrict such a hack to the known affected family.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1505,7 +1505,7 @@ static int svm_msr_read_intercept(unsign
         if ( rdmsr_safe(msr, *msr_content) == 0 )
             break;
 
-        if ( msr == MSR_F10_BU_CFG )
+        if ( boot_cpu_data.x86 == 0xf && msr == MSR_F10_BU_CFG )
         {
             /* Win2k8 x64 reads this MSR on revF chips, where it
              * wasn't publically available; it uses a magic constant