xen: no need for domU to worry about MCE/MCA

Mask MCE/MCA out of cpu caps.  Its harmless to leave them there, but
it does prevent the kernel from starting an unnecessary thread.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/xen/enlighten.c

@@ -155,6 +155,8 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 	if (*ax == 1)
 		maskedx = ~((1 << X86_FEATURE_APIC) |  /* disable APIC */
 			    (1 << X86_FEATURE_ACPI) |  /* disable ACPI */
+			    (1 << X86_FEATURE_MCE)  |  /* disable MCE */
+			    (1 << X86_FEATURE_MCA)  |  /* disable MCA */
 			    (1 << X86_FEATURE_ACC));   /* thermal monitoring */
 
 	asm(XEN_EMULATE_PREFIX "cpuid"