dt-bindings: display: ti,k2g-dss: Add dt-schema yaml binding

Add dt-schema yaml bindig for K2G DSS, an ultra-light version of TI
Keystone Display SubSystem.

Version history:

v2: no change

v3: - Add ports node
    - Add includes to dts example
    - reindent dts example

v4: - Add descriptions to reg and clocks properties
    - Remove minItems when its value is the same as maxItems value
    - Remove ports node

v5: - itemize reg and clocks properties' descriptions

v6: - Add Reviewed-by: from Rob Herring <robh@kernel.org> and
      Benoit Parrot <bparrot@ti.com>

v7: no change

v8: no change

v9: - Remove ports-node from the dts example
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/270297321f0768c10e241d289e3ac10e39cf12a9.1580129724.git.jsarha@ti.com

Documentation/devicetree/bindings/display/ti/ti,k2g-dss.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+# Copyright 2019 Texas Instruments Incorporated
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/display/ti/ti,k2g-dss.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Texas Instruments K2G Display Subsystem
+
+maintainers:
+  - Jyri Sarha <jsarha@ti.com>
+  - Tomi Valkeinen <tomi.valkeinen@ti.com>
+
+description: |
+  The K2G DSS is an ultra-light version of TI Keystone Display
+  SubSystem. It has only one output port and video plane. The
+  output is DPI.
+
+properties:
+  compatible:
+    const: ti,k2g-dss
+
+  reg:
+    items:
+      - description: cfg DSS top level
+      - description: common DISPC common
+      - description: VID1 video plane 1
+      - description: OVR1 overlay manager for vp1
+      - description: VP1 video port 1
+
+  reg-names:
+    items:
+      - const: cfg
+      - const: common
+      - const: vid1
+      - const: ovr1
+      - const: vp1
+
+  clocks:
+    items:
+      - description: fck DSS functional clock
+      - description: vp1 Video Port 1 pixel clock
+
+  clock-names:
+    items:
+      - const: fck
+      - const: vp1
+
+  interrupts:
+    maxItems: 1
+
+  power-domains:
+    maxItems: 1
+    description: phandle to the associated power domain
+
+  port:
+    type: object
+    description:
+      Port as described in Documentation/devictree/bindings/graph.txt.
+      The DSS DPI output port node
+
+  max-memory-bandwidth:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Input memory (from main memory to dispc) bandwidth limit in
+      bytes per second
+
+required:
+  - compatible
+  - reg
+  - reg-names
+  - clocks
+  - clock-names
+  - interrupts
+  - port
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    dss: dss@02540000 {
+            compatible = "ti,k2g-dss";
+            reg =   <0x02540000 0x400>,
+                    <0x02550000 0x1000>,
+                    <0x02557000 0x1000>,
+                    <0x0255a800 0x100>,
+                    <0x0255ac00 0x100>;
+            reg-names = "cfg", "common", "vid1", "ovr1", "vp1";
+            clocks =        <&k2g_clks 0x2 0>,
+                            <&k2g_clks 0x2 1>;
+            clock-names = "fck", "vp1";
+            interrupts = <GIC_SPI 247 IRQ_TYPE_EDGE_RISING>;
+
+            power-domains = <&k2g_pds 0x2>;
+
+            max-memory-bandwidth = <230000000>;
+
+            port {
+                    dpi_out: endpoint {
+                            remote-endpoint = <&sii9022_in>;
+                    };
+            };
+    };