dt-bindings: drm/bridge: adv7511: Add regulator bindings

Add the regulator supply properties needed by ADV7511 and ADV7533. The
regulator names are named after the pin names, except for DVDD_3V on
ADV7511, which is left v3p3 to have the same name as it's on ADV7533.

ADV7511 has a BGVDD pin for which the voltage to be configured isn't
clear. This needs to be updated in the document later.

The regulators are specified as optional properties since there can
be boards which have a fixed supply directly routed to the pins, and
these may not be modelled as regulator supplies.

Cc: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Archit Taneja <architt@codeaurora.org>