firmware: dmi_scan: Add DMI_OEM_STRING support to dmi_matches

OEM strings are defined by each OEM and they contain customized and
useful OEM information. Supporting it provides more flexible uses of
the dmi_matches function.

Signed-off-by: Alex Hung <alex.hung@canonical.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 48fb2b43..7d361be 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -502,6 +502,7 @@ enum dmi_field {
 	DMI_CHASSIS_SERIAL,
 	DMI_CHASSIS_ASSET_TAG,
 	DMI_STRING_MAX,
+	DMI_OEM_STRING,	/* special case - will not be in dmi_ident */
 };
 
 struct dmi_strmatch {