kernel: move old firmware uimage splitter into separated patch

This will allow us to drop it in the future. This patch doesn't change
the final mtdpart.c, it remains the same.

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


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43696 3c298f89-4303-0410-b956-a3cf2f4a3e73