dfu, nand, ubi: add partubi alt settings for updating ubi partition

updating an ubi partition needs a completely erased mtd partition,
see:
http://lists.infradead.org/pipermail/linux-mtd/2011-May/035416.html

So, add partubi alt setting for the dfu_alt_info environment
variable to mark this partition as an ubi partition. In case we
update an ubi partition, we erase after flashing the image into the
partition, the remaining sektors.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Cc: Tom Rini <trini@ti.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Scott Wood <scottwood@freescale.com>

include/dfu.h

@@ -47,6 +47,8 @@ struct nand_internal_data {
 
 	unsigned int dev;
 	unsigned int part;
+	/* for nand/ubi use */
+	unsigned int ubi;
 };
 
 static inline unsigned int get_mmc_blk_size(int dev)