dt-bindings: timer: fsl,imxgpt: Add optional osc_per clock

Since commit bad3db104f ("ARM: imx: source gpt per clk from OSC for
system timer") osc_per can be used for clocking the GPT which is not
scaled when entering low bus mode.
This clock source is available only on i.MX6Q (incl. i.MX6QP) and i.MX6DL.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230810144451.1459985-7-alexander.stein@ew.tq-group.com
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/timer/fsl,imxgpt.yaml

@@ -46,14 +46,18 @@ properties:
     maxItems: 1
 
   clocks:
+    minItems: 2
     items:
       - description: SoC GPT ipg clock
       - description: SoC GPT per clock
+      - description: SoC GPT osc per clock
 
   clock-names:
+    minItems: 2
     items:
       - const: ipg
       - const: per
+      - const: osc_per
 
 required:
   - compatible
@@ -62,6 +66,29 @@ required:
   - clocks
   - clock-names
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - fsl,imx6dl-gpt
+              - fsl,imx6q-gpt
+    then:
+      properties:
+        clocks:
+          minItems: 2
+          maxItems: 3
+        clock-names:
+          minItems: 2
+          maxItems: 3
+    else:
+      properties:
+        clocks:
+          maxItems: 2
+        clock-names:
+          maxItems: 2
+
 additionalProperties: false
 
 examples: