If there's enough information to have Linux on it, porting OpenBSD to it involves less intensive reverse engineering. The Mesa drivers run in userspace, so if a compatible OpenBSD KMS driver for the Vivante is made, you can run the same userspace graphics stack.

i.MX6 support was added in September 2013. I don't think there's i.MX8 support yet, but it's probably not a herculean task to get it running.