initramfs-kexecboot-image: fix dependency chain was: ['ubiattach']

* unfortunately there is no package-split for the mtd-utils recipe
* to have ubiattach we need to install the full package
* (or use ubiattach-klibc)

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>