drm/gk208/gr: add missing registers to grctx init

This fixes hangs on GK208 which happen instantaneously on trying to use a
geometry shader.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org # v3.14+