dt-bindings: serial: renesas,em-uart: Add RZ/V2M clock to access the registers

The RZ/V2M SoC has an additional clock to access the registers. The HW
manual says this clock should not be touched as it is used by the
"ISP Firmware".

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Link: https://lore.kernel.org/r/20220512072649.7879-1-phil.edworthy@renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/renesas,em-uart.yaml

@@ -9,9 +9,6 @@ title: Renesas EMMA Mobile UART Interface
 maintainers:
   - Magnus Damm <magnus.damm@gmail.com>
 
-allOf:
-  - $ref: serial.yaml#
-
 properties:
   compatible:
     oneOf:
@@ -30,10 +27,31 @@ properties:
     maxItems: 1
 
   clocks:
-    maxItems: 1
+    minItems: 1
+    items:
+      - description: UART functional clock
+      - description: Internal clock to access the registers
 
   clock-names:
-    const: sclk
+    minItems: 1
+    items:
+      - const: sclk
+      - const: pclk
+
+allOf:
+  - $ref: serial.yaml#
+
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: renesas,r9a09g011-uart
+    then:
+      properties:
+        clocks:
+          minItems: 2
+        clock-names:
+          minItems: 2
 
 required:
   - compatible