This patch adds support for "kwbimage" (Kirkwood Boot Image)
image types to the mkimage code.

For details refer to docs/README.kwbimage

This patch is tested with Sheevaplug board

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>
Acked-by: Ron Lee <ron@debian.org>

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>