This commit adds "hex pattern mode" to xorimage. This mode allows xor
with a hexadecimal pattern that cannot be expressed with ASCII
charactors.

usage (example):
  xorimage -i firmware.bin -o firmware.bin.new -p 6A57190601121E4C -x

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com> (fix checkpatch)