We have been unable to replicate this with the latest AMD GPU firmware from
https://people.freedesktop.org/~agd5f/radeon_ucode/polaris/ .  Xorg starts fine
with no errors.

System: Debian Testing
Kernel: 4.17.0-rc6

$ getconf PAGESIZE
65536

If you still experience the issues please give detailed instructions on how to
reproduce your test environment, including OS installed and packages /
configuration files in use.