mtd: uclass: add probe function

The user might want to trigger the probe of any MTD device, export these
functions so they can be called from a command source file.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/include/mtd.h b/include/mtd.h
index 9e5c807..75aca26 100644
--- a/include/mtd.h
+++ b/include/mtd.h
@@ -8,4 +8,6 @@
 
 #include <linux/mtd/mtd.h>
 
+int mtd_probe(struct udevice *dev);
+
 #endif	/* _MTD_H_ */