R9285 since below testing amd-staging-4.6/7 I lock on boot as soon as drm
loads.

No logging, no sysrq, no display, flashing keyboard.

commit bbc6372f92db837ef30f41eced850c08d91a3ebb
Author: Joshua Aberback <Joshua.Aberback@amd.com>
Date:   Tue Jul 26 11:58:06 2016 -0400

    drm/amd/dal: track display state based on sink and stream for freesync

    This is to avoid problems with arrays out of bounds when OS calls
    a flip on a display that's been removed but on which reset_mode
    has not been called yet.