drm/radeon/kms: add HDP flushing for all GPUs.

rendercheck under kms on r600s was failing due to HDP flushing not happening.

This adds HDP flushing to the object wait function for r100->r700 families.

rendercheck passes basic tests on r600 with this change.

Acked-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>