dt-bindings: trivial-devices: Allow 'spi-max-frequency' property

Trivial SPI devices can also specify 'spi-max-frequency' properties, so
allow it in the trivial devices schema.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210316194939.3529018-1-robh@kernel.org

Documentation/devicetree/bindings/trivial-devices.yaml

@@ -23,6 +23,9 @@ properties:
     maxItems: 1
   interrupts:
     maxItems: 1
+
+  spi-max-frequency: true
+
   compatible:
     items:
       - enum: