drm/radeon/kms/evergreen: always set certain VGT regs at CP init

These should be handled by the clear_state setup, but set them
directly as well just to be sure.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>