firmware: dmi: Add access to the SKU ID string

This is used in some systems from user space for determining the identity
of the device.

Expose this as a file so that that user-space tools don't need to read
from /sys/firmware/dmi/tables/DMI

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Jean Delvare <jdelvare@suse.de>
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 7d361be..61fbfbc 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -490,6 +490,7 @@ enum dmi_field {
 	DMI_PRODUCT_VERSION,
 	DMI_PRODUCT_SERIAL,
 	DMI_PRODUCT_UUID,
+	DMI_PRODUCT_SKU,
 	DMI_PRODUCT_FAMILY,
 	DMI_BOARD_VENDOR,
 	DMI_BOARD_NAME,