dt-bindings: display/msm: drop assigned-clock-parents for dp controller

DP controller schema documents assigned-clocks and
assigned-clock-parents. However these assignments should not be a part
of the ABI: there are no actual requirements on the order of the
assignments, MST cases require different number of clocks to be
assigned, etc.

Instead of fixing up the documentation, drop the assigned-clock-parents
and assigned-clocks from the bindings. The generic clock/clock.yaml
already covers these properties.

Suggested-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Abhinav Kumar <[e-mail]>
Signed-off-by: Jessica Zhang <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Dmitry Baryshkov <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/672586/
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/display/msm/dp-controller.yaml

···
       - const: ctrl_link_iface
       - const: stream_pixel
 
-  assigned-clocks:
-    items:
-      - description: link clock source
-      - description: pixel clock source
-
-  assigned-clock-parents:
-    items:
-      - description: phy 0 parent
-      - description: phy 1 parent
-
   phys:
     maxItems: 1