tools/kwbimage: fix size computations for v1 images

Fix computation of haeder size and binary header size.
Size of opt header and some 32bit values were not taken into account. This could
result in invalid boot images (due to the wrong binary header size, the image could
claim to have another extension header after the binary extension although there
is none).

Use "uint32_t" instead of "unsigned int" for header size computation.

Signed-off-by: Reinhard Pfau <reinhard.pfau@gdsys.cc>
Reviewed-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>