dm: extcon: add an uclass for extcon

Add a new simple uclass for extcon. Currently all setup is done
in the probe. Uclass struct and ops are empty for now.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/uclass-id.h b/include/dm/uclass-id.h
index 5386c3fa..307ad69 100644
--- a/include/dm/uclass-id.h
+++ b/include/dm/uclass-id.h
@@ -56,6 +56,7 @@
 	UCLASS_EFI_MEDIA,	/* Devices provided by UEFI firmware */
 	UCLASS_ETH,		/* Ethernet device */
 	UCLASS_ETH_PHY,		/* Ethernet PHY device */
+	UCLASS_EXTCON,		/* External Connector Class */
 	UCLASS_FIRMWARE,	/* Firmware */
 	UCLASS_FPGA,		/* FPGA device */
 	UCLASS_FUZZING_ENGINE,	/* Fuzzing engine */