ACPI / scan: introduce platform_id device PNP type flag

Only certain types of ACPI device objects can be enumerated as
platform devices, so in order to distinguish them from the others
introduce a new ACPI device PNP type flag, platform_id, and set it
for devices with a valid _HID to start with.

This change is based on a Zhang Rui's prototype.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 19d524c..ebbd23c 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -1797,8 +1797,10 @@
 			return;
 		}
 
-		if (info->valid & ACPI_VALID_HID)
+		if (info->valid & ACPI_VALID_HID) {
 			acpi_add_id(pnp, info->hardware_id.string);
+			pnp->type.platform_id = 1;
+		}
 		if (info->valid & ACPI_VALID_CID) {
 			cid_list = &info->compatible_id_list;
 			for (i = 0; i < cid_list->count; i++)