Minor coding style cleanup.

Signed-off-by: Wolfgang Denk <wd@denx.de>

mkimage: add UBL header support for booting davinci cpus

creating an u-boot.ubl file, which contains the UBL Header
needed for booting from NAND with the RBL from TI. For more
information read doc/README.ublimage.

Signed-off-by: Heiko Schocher <hs@denx.de>