[ACPI] Prefer _CST over FADT for C-state capabilities

Note: This ACPI standard compliance may cause regression
on some system, if they have _CST present, but _CST value
is bogus. "nocst" module parameter should workaround
that regression.

http://bugzilla.kernel.org/show_bug.cgi?id=5165

Signed-off-by: Venkatesh Pallipadi<venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
(cherry picked from 883baf7f7e81cca26f4683ae0d25ba48f094cc08 commit)

drivers/acpi/processor_idle.c

@@ -690,7 +690,7 @@ static int acpi_processor_get_power_info_cst(struct acpi_processor *pr)
 
 	/* Validate number of power states discovered */
 	if (pr->power.count < 2)
-		status = -ENODEV;
+		status = -EFAULT;
 
       end:
 	acpi_os_free(buffer.pointer);
@@ -841,11 +841,11 @@ static int acpi_processor_get_power_info(struct acpi_processor *pr)
 	 * this function */
 
 	result = acpi_processor_get_power_info_cst(pr);
-	if ((result) || (acpi_processor_power_verify(pr) < 2)) {
+	if (result == -ENODEV)
 		result = acpi_processor_get_power_info_fadt(pr);
+
 	if ((result) || (acpi_processor_power_verify(pr) < 2))
 		result = acpi_processor_get_power_info_default_c1(pr);
-	}
 
 	/*
 	 * Set Default Policy