Hello Nathan Holder,
There are two alternatives:
BSP Releases: Latest is 4.9.11 and it supports the i.MX6ULL among other NXP boards as defined in the BSP documentation. For information on how to download and setup this BSP please look at the BSP documentation (link below)
https://www.nxp.com/webapp/Download?colCode=L4.9.11_1.0.0_LINUX_DOCS
The repo for this BSP is:
$ repo init -u git://git.freescale.com/imx/fsl-arm-yocto-bsp.git -b imx-morty
Community BSP: This is part of the Yocto Project and includes support for third party boards. All information on how to download and setup as well as documentation is available on the link below:
http://freescale.github.io/
In this case the repo would depend on the branch used, for morty would be:
$ repo init -u https://github.com/Freescale/fsl-community-bsp-platform -b morty
I hope this information helps!
Regards,