drm/radeon: Explicitly print GTT/VRAM offsets on test failure.

Otherwise these would need to be painstakingly calculated looking at the source
code.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>