tools: kwbimage: Dump kwbimage config file on '-p -1' option

To regenerate kwbimage from existing image, it is needed to have kwbimage
config file. Add a new option to generate kwbimage config file from
existing kwbimage when '-p 1' option is given.

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