firmware-utils: add oseama tool for creating Seama entities

firmware-utils: add oseama tool for creating Seama entities

It has an important feature (compared to seama) of using multiple input
files, aligning them and padding zeroes until reaching a specified
absolute offset. This is needed for a proper flash layout on NAND. We
want kernel partition to be big enough to handle future updates without
a need to resize it and wipe whole "ubi" partition. It's important as
we don't want to lose block counters.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Backport of r48601

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@49116 3c298f89-4303-0410-b956-a3cf2f4a3e73