dt-bindings: display: vc4: dsi: Add missing clock properties

While the device tree and the driver expected a clock-names and a
clock-cells properties, it wasn't explicitly documented in the previous
binding. Make sure it is now.

Cc: devicetree@vger.kernel.org
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/867813ae6b3e9cff0e9627e6ed09569dee5573bc.1590594512.git-series.maxime@cerno.tech

Documentation/devicetree/bindings/display/brcm,bcm2835-dsi0.yaml

@@ -10,6 +10,9 @@ maintainers:
   - Eric Anholt <eric@anholt.net>
 
 properties:
+  "#clock-cells":
+    const: 1
+
   compatible:
     enum:
       - brcm,bcm2835-dsi0
@@ -24,6 +27,12 @@ properties:
       - description: The DSI ESC clock
       - description: The DSI pixel clock
 
+  clock-names:
+    items:
+      - const: phy
+      - const: escape
+      - const: pixel
+
   clock-output-names: true
     # FIXME: The meta-schemas don't seem to allow it for now
     # items:
@@ -35,9 +44,11 @@ properties:
     maxItems: 1
 
 required:
+  - "#clock-cells"
   - compatible
   - reg
   - clocks
+  - clock-names
   - clock-output-names
   - interrupts