pc: add SMM property

The property can take values on, off or auto.  The default is "off"
for KVM and pre-2.4 machines, otherwise "auto" (which makes it
available on TCG or on new-enough kernels).

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target-i386/kvm-stub.c

@@ -18,6 +18,11 @@ bool kvm_allows_irq0_override(void)
 }
 
 #ifndef __OPTIMIZE__
+bool kvm_has_smm(void)
+{
+    return 1;
+}
+
 /* This function is only called inside conditionals which we
  * rely on the compiler to optimize out when CONFIG_KVM is not
  * defined.