package and booting an initramfs image

Embedded 1

I have a need to package my kernel, dtb, and rootfs manually and then boot this as an initramfs. I'm not sure which files from the deploy/images directory to use. I see there is an rootfs.cpio.gz file so I'm starting with that. If I unpack that I see the kernel Image and dtb in the /boot folder and what appears to be a filesystem in the rest. If I try to boot this as my kernel in u-boot I get this
Bad Linux ARM64 Image magic!
** No partition table - mmc 2 **
** No partition table - mmc 2 **

Does this cpio.gz file have everything I need? How do I boot with it and enter an initramfs?

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