Subject: ACPI: allow passing down C1 information if no other C-states exist

Otherwise Xen may end up not using MWAIT despite its availability.

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

--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -780,7 +780,7 @@ static int acpi_processor_get_power_info
 			  current_count));
 
 	/* Validate number of power states discovered */
-	if (current_count < 2)
+	if (current_count < 1 + !processor_pm_external())
 		status = -EFAULT;
 
       end: