ACPI / processor: Set P_LVL{2,3} idle state descriptions

The ACPI idle driver will fallback to using the legacy P_LVL* SystemIO
method of entering C-states if the _CST method is disabled and P_BLK is
defined. However, in this case the C2 and C3 states won't have a
description set, so the user will see "<null>" when reading the
description from sysfs.

Give each of these states a description.
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/processor_idle.c

@@ -282,6 +282,13 @@ static int acpi_processor_get_power_info_fadt(struct acpi_processor *pr)
 			  pr->power.states[ACPI_STATE_C2].address,
 			  pr->power.states[ACPI_STATE_C3].address));
 
+	snprintf(pr->power.states[ACPI_STATE_C2].desc,
+			 ACPI_CX_DESC_LEN, "ACPI P_LVL2 IOPORT 0x%x",
+			 pr->power.states[ACPI_STATE_C2].address);
+	snprintf(pr->power.states[ACPI_STATE_C3].desc,
+			 ACPI_CX_DESC_LEN, "ACPI P_LVL3 IOPORT 0x%x",
+			 pr->power.states[ACPI_STATE_C3].address);
+
 	return 0;
 }