The VDD supply is only needed to supply power to eDP panels connected to
DPAUX. Technically that supply should be dealt with in the panel driver,
but for backwards-compatibility we need to keep this around anyway.

Also as a bit of background: the reason for why this supply is attached
to DPAUX is to make sure the panel is properly powered early on so that
it can generate a hotplug pulse at the appropriate time. This may no
longer be required given the support for deferred fbdev setup that was
"recently" introduced in DRM/KMS.
Signed-off-by: Thierry Reding <treding@nvidia.com>