drm/tegra: hdmi - Add connector supply support

Revert commit 18ebc0f4 "drm/tegra: hdmi: Enable VDD earlier for
hotplug/DDC" and instead add a new supply for the +5V pin on the HDMI
connector.

The vdd-supply property refers to the regulator that supplies the
AVDD_HDMI input on Tegra, rather than the +5V HDMI connector pin. This
was never a problem before, because all boards had that pin hooked up to
a regulator that was always on. Starting with Dalmore and continuing
with Venice2, the +5V pin is controllable via a GPIO. For reasons
unknown, the GPIO ended up as the controlling GPIO of the AVDD_HDMI
supply in the Dalmore and Venice2 DTS files. But that's not correct.
Instead, a separate supply must be introduced so that the +5V pin can be
controlled separately from the supplies that feed the HDMI block within
Tegra.

A new hdmi-supply property is introduced that takes the place of the
vdd-supply and vdd-supply is only enabled when HDMI is enabled rather
than all the time.

Signed-off-by: Thierry Reding <treding@nvidia.com>