tools/kwboot: Sync with latest barebox version to support Armada XP

The barebox version of the kwboot tool has evolved a bit. To support
Armada XP and Dove. Additionally a few minor fixes have been applied.
So lets sync with the latest barebox version.

Please note that the main difference between both versions now is, that
the U-Boot version still supports the -p option, to dynamically patch
an image for UART boot mode. I didn't test it now though.

Signed-off-by: Stefan Roese <sr@denx.de>
Tested-by: Luka Perkov <luka@openwrt.org>