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>

include/extcon.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2023 Svyatoslav Ryhel <clamor95@gmail.com>
+ */
+
+#ifndef __EXTCON_H
+#define __EXTCON_H
+
+struct udevice;
+
+/**
+ * struct extcon_uc_plat - Platform data the uclass stores about each device
+ *
+ * To be filled
+ */
+struct extcon_uc_plat {
+};
+
+#endif