dt-bindings: msm: dsi-controller-main: Add vdd* descriptions back in

When converting from .txt to .yaml we didn't include descriptions for the
existing regulator supplies.

- vdd
- vdda
- vddio

Add those descriptions into the yaml now as they were prior to the
conversion. In the .txt description we marked these regulators as required,
however, that requirement appears to have been in error.

Taking the example of sc7180-trogdor-wormdingler.dtsi. The avdd and avee
come from GPIO controlled external regulators, not the SoC and in this case
there's no need for vddio to power an I/O bus. Similarly the regulators for
the LCD are controlled by the panel driver not by the dsi-ctrl driver.

It would be possible to connect a different type of panel to the DSI bus
here in which case we may or may not want to make use of vdd, vdda or
vddio.

This is also the case for older chipsets like apq8064, msm8916 etc the vdd*
regulators in the dsi-ctrl block are helpers not dependencies.

Add the description of vdd, vdda and vddio back in for the existing
upstream dts where vdd, vdda or vddio are already declared but, don't
declare those regulators required - they are not SoC requirements.

Fixes: 4dbe55c9 ("dt-bindings: msm: dsi: add yaml schemas for DSI bindings")
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/518643/
Link: https://lore.kernel.org/r/20230116225217.1056258-4-bryan.odonoghue@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Documentation/devicetree/bindings/display/msm/dsi-controller-main.yaml

@@ -127,6 +127,18 @@ properties:
       - port@0
       - port@1
 
+  vdd-supply:
+    description:
+      VDD regulator
+
+  vddio-supply:
+    description:
+      VDD-IO regulator
+
+  vdda-supply:
+    description:
+      VDDA regulator
+
 required:
   - compatible
   - reg