Currently, users of Mediatek UFOe (Unified Frame Optimization engine) DT
bindings set mediatek,gce-client-reg node property, which is missing from
the DT schema.

For example, device tree arch/arm64/boot/dts/mediatek/mt8173.dtsi is
causing the following dtb check error:

```
$ make CHECK_DTBS=y mediatek/mt8173-elm.dtb
   SCHEMA  Documentation/devicetree/bindings/processed-schema.json
   DTC [C] arch/arm64/boot/dts/mediatek/mt8173-elm.dtb
[...]
arch/arm64/boot/dts/mediatek/mt8173-elm.dtb: ufoe@1401a000
(mediatek,mt8173-disp-ufoe): 'mediatek,gce-client-reg' does not match
any of the regexes: '^pinctrl-[0-9]+$'
```

This commit adds the missing node property in the DT schema and updates the
example as well.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>
---
 .../bindings/display/mediatek/mediatek,ufoe.yaml  | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/mediatek/mediatek,ufoe.yaml b/Documentation/devicetree/bindings/display/mediatek/mediatek,ufoe.yaml
index 61a5e22effbf2..036a66ed42e73 100644
--- a/Documentation/devicetree/bindings/display/mediatek/mediatek,ufoe.yaml
+++ b/Documentation/devicetree/bindings/display/mediatek/mediatek,ufoe.yaml
@@ -64,6 +64,18 @@ properties:
       - port@0
       - port@1
 
+  mediatek,gce-client-reg:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    description: describes how to locate the GCE client register
+    items:
+      - items:
+          - description: Phandle reference to a Mediatek GCE Mailbox
+          - description:
+              GCE subsys id mapping to a client defined in header
+              include/dt-bindings/gce/<chip>-gce.h.
+          - description: offset for the GCE register offset
+          - description: size of the GCE register offset
+
 required:
   - compatible
   - reg
@@ -77,7 +89,9 @@ examples:
   - |
     #include <dt-bindings/interrupt-controller/arm-gic.h>
     #include <dt-bindings/clock/mt8173-clk.h>
+    #include <dt-bindings/gce/mt8173-gce.h>
     #include <dt-bindings/power/mt8173-power.h>
+
     soc {
         #address-cells = <2>;
         #size-cells = <2>;
@@ -88,5 +102,6 @@ examples:
             interrupts = <GIC_SPI 191 IRQ_TYPE_LEVEL_LOW>;
             power-domains = <&scpsys MT8173_POWER_DOMAIN_MM>;
             clocks = <&mmsys CLK_MM_DISP_UFOE>;
+            mediatek,gce-client-reg = <&gce SUBSYS_1401XXXX 0xa000 0x1000>;
         };
     };
-- 
2.50.1