drm/amdgpu: don't free conflicting apertures for non-display devices

PCI_CLASS_ACCELERATOR_PROCESSING devices won't ever be
the sysfb, so there is no need to free conflicting
apertures.

Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>