AFAIK, video driver doesn't have anything to do with the mappings.  Does
forcing a modeset after resume help?  E.g., change the mode with xrandr and see
if that helps.  Maybe some of the AMD specific verbs in the hda driver need to
be reset?

http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/10/AMD_HDA_verbs_v2.pdf