Revert "[patches] remove 006-target-imagebuilder-remove-initramfs-dep.patch"

This reverts commit d7cf86fc4a94a6bf2a636ee02b44764b61a55214.
Seems it is still necessary (see http://buildbot.berlin.freifunk.net/builders/
ar71xx_mikrotik/builds/209/steps/shell/logs/stdio)