linux-phytec-ti

drm/nouveau/platform: make VDD regulator optional

GP10B's power is managed by generic PM domains, so it does not require a
VDD regulator. Add this option into the chip function structure.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>