initramfs.cpio.gz is generate by ltib.
You can run ltib to choose mfgtool profile.
ltib will build initramfs.cpio.gz for you.
You can choose what package need build-in initramfs.cpio.gz by ltib.
The components depend on your user case.
Generally, uuc, kobs-ng, udev, mtd-utils, busy-box must be in initramfs.cpio.gz