dfu: add partition support for MTD backend

Add the support of MTD partition for the MTD backend.

The expected dfu_alt_info for one alternate on the mtd device :
	<name> part <part_id>
        <name> partubi <part_id>

"partubi" also erase up to the end of the partition after write operation.

For example: dfu_alt_info = "spl part 1;u-boot part 2; UBI partubi 3"

U-Boot> dfu 0 mtd nand0

Acked-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>

include/dfu.h

@@ -62,6 +62,8 @@ struct mtd_internal_data {
 	/* RAW programming */
 	u64 start;
 	u64 size;
+	/* for ubi partition */
+	unsigned int ubi;
 };
 
 struct nand_internal_data {