Sorry, Maybe I'm not clear enough.
When I talk about 'Buildroot'，I really mean the OpenWRT building enviroment.
So, Is there anywhere to download the iMX6.Ul's OpenWRT building enviroment?
Ok, then discard my comment, Buildroot and OpenWRT are completely different now.
As for OpenWRT, the mainline version doesn't seem to support this CPU.
Well I'm no NXP employee so I can't help you with the sources of that demo.
I only tried to help because I maintain i.MX6 support in Buildroot.
Regarding OpenWRT, I guess you just need to update the kernel "recipe" to use the latest 4.1.15 one from NXP. But I won't be able to help you any further, good luck!
Yes, I have checked the OpenWRT github repo, and found that doesn't support this CPU.
When I search more from internet, Google lead me to this content, https://community.nxp.com/docs/DOC-331175 ,
It seems that your guys has ported this CPU to OpenWRT, so that's why I'm seeking help in community.