dt-bindings: mfd: x-powers,axp152: Document the AXP313a variant

The X-Powers AXP313a is a PMIC used on some devices with the Allwinner
H616 or H313 SoC.

According to the datasheet, the DC/DC converter PWM frequency is fixed
(to 3 MHz), so disallow the property that lets us set this frequency
for the other PMICs.

Signed-off-by: Martin Botka <martin.botka@somainline.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230401001850.4988-2-andre.przywara@arm.com
(cherry picked from commit 2a9e8a1a7c4caadf690e5a77fe4162c5edab4a9c)
Signed-off-by: Lee Jones <lee@kernel.org>

Documentation/devicetree/bindings/mfd/x-powers,axp152.yaml

@@ -73,6 +73,16 @@ allOf:
       required:
         - interrupts
 
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: x-powers,axp313a
+
+    then:
+      properties:
+        x-powers,dcdc-freq: false
+
 properties:
   compatible:
     oneOf:
@@ -82,6 +92,7 @@ properties:
           - x-powers,axp209
           - x-powers,axp221
           - x-powers,axp223
+          - x-powers,axp313a
           - x-powers,axp803
           - x-powers,axp806
           - x-powers,axp809