The checksum at predefined offset is required for execution of images
from the LPC178X eNVM. This patch automates the creation of this
checksum, the resulted images are u-boot-lpc.bin and u-boot-lpc.hex.

File is taken from pollux.denx.org:/home/git/u-boot/ tree.
Signed-off-by: Yuri Tikhonov <yur@emcraft.com>