drm/radeon: allow geom rings to be setup on r600/r700 (v2)
the evergreen CS parser has allowed this for a while, just port
the code to the r600 one.
This is required before geom shaders can be made work.
v2: agd5f: minor cleanup and add additional 7xx reg.
Signed-off-by: Dave Airlie <airlied@redhat.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Dave Airlie <airlied@redhat.com>