tools: dumpimage: Show error message when trying to extract data from kwbimage

There is no code for extracting data from kwbimage, so show an error
message when user tries this via e.g. dumpimage call:
  ./tools/dumpimage -T kwbimage -o /tmp/out u-boot-spl.kwb

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
1 file changed