dt-bindings: display: add Unisoc's dpu bindings

DPU (Display Processor Unit) is the Display Controller for the Unisoc SoCs
which transfers the image data from a video memory buffer to an internal
LCD interface.

Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Signed-off-by: Kevin Tang <kevin.tang@unisoc.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211207142717.30296-4-kevin3.tang@gmail.com

Documentation/devicetree/bindings/display/sprd/sprd,sharkl3-dpu.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/sprd/sprd,sharkl3-dpu.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Unisoc Sharkl3 Display Processor Unit (DPU)
+
+maintainers:
+  - Kevin Tang <kevin.tang@unisoc.com>
+
+description: |
+  DPU (Display Processor Unit) is the Display Controller for the Unisoc SoCs
+  which transfers the image data from a video memory buffer to an internal
+  LCD interface.
+
+properties:
+  compatible:
+    const: sprd,sharkl3-dpu
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    minItems: 2
+
+  clock-names:
+    items:
+      - const: clk_src_128m
+      - const: clk_src_384m
+
+  power-domains:
+    maxItems: 1
+
+  iommus:
+    maxItems: 1
+
+  port:
+    type: object
+    description:
+      A port node with endpoint definitions as defined in
+      Documentation/devicetree/bindings/media/video-interfaces.txt.
+      That port should be the output endpoint, usually output to
+      the associated DSI.
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+  - port
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/clock/sprd,sc9860-clk.h>
+    dpu: dpu@63000000 {
+        compatible = "sprd,sharkl3-dpu";
+        reg = <0x63000000 0x1000>;
+        interrupts = <GIC_SPI 46 IRQ_TYPE_LEVEL_HIGH>;
+        clock-names = "clk_src_128m", "clk_src_384m";
+
+        clocks = <&pll CLK_TWPLL_128M>,
+          <&pll CLK_TWPLL_384M>;
+
+        dpu_port: port {
+            dpu_out: endpoint {
+                remote-endpoint = <&dsi_in>;
+            };
+        };
+    };