This reverts commit 9ed2c993.

SET_CONFIG_REG writes to memory if register shadowing is enabled,
causing a VM fault.

NGG streamout is unstable anyway, so all UMDs should use legacy
streamout. I think Mesa is the only driver using NGG streamout.
Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Le Ma <Le.Ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>