dt-bindings: net: dp83822: support configuring RMII master/slave mode

Add property ti,rmii-mode to support selecting the RMII operation mode
between:
	- master mode (PHY operates from a 25MHz clock reference)
	- slave mode (PHY operates from a 50MHz clock reference)

If not set, the operation mode is configured by hardware straps.
Signed-off-by: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/ti,dp83822.yaml

@@ -80,6 +80,22 @@ properties:
            10625, 11250, 11875, 12500, 13125, 13750, 14375, 15000]
     default: 10000
 
+  ti,rmii-mode:
+    description: |
+       If present, select the RMII operation mode. Two modes are
+       available:
+         - RMII master, where the PHY operates from a 25MHz clock reference,
+         provided by a crystal or a CMOS-level oscillator
+         - RMII slave, where the PHY operates from a 50MHz clock reference,
+         provided by a CMOS-level oscillator
+       The RMII operation mode can also be configured by its straps.
+       If the strap pin is not set correctly or not set at all, then this can be
+       used to configure it.
+    $ref: /schemas/types.yaml#/definitions/string
+    enum:
+      - master
+      - slave
+
 required:
   - reg