tools: kwbimage: Remove v1 kwbimage SPL padding to CONFIG_SYS_U_BOOT_OFFS bytes

tools: kwbimage: Remove v1 kwbimage SPL padding to CONFIG_SYS_U_BOOT_OFFS bytes

This padding depends on board config file and therefore it makes the
mkimage binary tool board specific, which is not correct. One cannot use
mkimage tool built as a result for board A to generate images for board
B, even if both A and B are on the same platform.

This CONFIG_SYS_U_BOOT_OFFS padding was needed when kwbimage v1 contained
SPL code which loaded U-Boot proper based on CONFIG_SYS_U_BOOT_OFFS,
instead of reading correct offset from kwbimage header.

Now that SPL code parses kwbimage header and deterinate correct offset,
there is no need for this CONFIG_SYS_U_BOOT_OFFS padding anymore.

By removing it we also reduce the size of SPL code and therefore also
decrease the final size of v1 kwbimage. This means there is more space
for U-Boot proper binary.

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