dt-bindings: allwinner: add H616 DE33 mixer binding

The Allwinner H616 and variants have a new display engine revision
(DE33).

The mixer configuration registers are significantly different to the DE3
and DE2 revisions, being split into separate top and display blocks,
therefore a fallback for the mixer compatible is not provided.

Note that the DE33 mixer requires 3 register blocks instead of 1. To
keep things simple the maxItems value for registers is conditionally
removed for the H616 and replaced with the block names from the vendor
BSP kernel.

Add a display engine mixer binding for the DE33.

Signed-off-by: Ryan Walklin <ryan@testtoast.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Link: https://lore.kernel.org/r/20250528092431.28825-6-ryan@testtoast.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>

Documentation/devicetree/bindings/display/allwinner,sun8i-a83t-de2-mixer.yaml

@@ -24,9 +24,11 @@ properties:
       - allwinner,sun50i-a64-de2-mixer-0
       - allwinner,sun50i-a64-de2-mixer-1
       - allwinner,sun50i-h6-de3-mixer-0
+      - allwinner,sun50i-h616-de33-mixer-0
 
-  reg:
-    maxItems: 1
+  reg: true
+
+  reg-names: true
 
   clocks:
     items:
@@ -61,6 +63,34 @@ properties:
     required:
       - port@1
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - allwinner,sun50i-h616-de33-mixer-0
+    then:
+      properties:
+        reg:
+          description: |
+            Registers for controlling individual layers of the display
+            engine (layers), global control (top), and display blending
+            control (display). Names are from Allwinner BSP kernel.
+          maxItems: 3
+        reg-names:
+          items:
+            - const: layers
+            - const: top
+            - const: display
+      required:
+        - reg-names
+
+    else:
+      properties:
+        reg:
+          maxItems: 1
+
 required:
   - compatible
   - reg