dt-bindings: display: ti,j721e-dss: add missing properties to dt-schema

Add assigned-clocks, assigned-clock-parents and dma-coherent optional
properties.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200916131009.221252-3-tomi.valkeinen@ti.com

Documentation/devicetree/bindings/display/ti/ti,j721e-dss.yaml

@@ -77,6 +77,14 @@ properties:
       - const: vp3
       - const: vp4
 
+  assigned-clocks:
+    minItems: 1
+    maxItems: 5
+
+  assigned-clock-parents:
+    minItems: 1
+    maxItems: 5
+
   interrupts:
     items:
       - description: common_m DSS Master common
@@ -95,6 +103,9 @@ properties:
     maxItems: 1
     description: phandle to the associated power domain
 
+  dma-coherent:
+    type: boolean
+
   ports:
     type: object
     description: