drm/nv40: Init some tiling-related PGRAPH state.

Fixes garbled 3D on an nv46 card.

Reported-by: Francesco Marella <francesco.marella@gmail.com>
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>