dt-bindings: net: renesas,etheravb: Add additional clocks

The AVB driver assumes there is an external crystal, but it could
be clocked by other means.  In order to enable a programmable
clock, it needs to be added to the clocks list and enabled in the
driver.  Since there currently only one clock, there is no
clock-names list either.

Update bindings to add the additional optional clock, and explicitly
name both of them.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/renesas,etheravb.yaml

@@ -50,7 +50,16 @@ properties:
   interrupt-names: true
 
   clocks:
-    maxItems: 1
+    minItems: 1
+    maxItems: 2
+    items:
+      - description: AVB functional clock
+      - description: Optional TXC reference clock
+
+  clock-names:
+    items:
+      - const: fck
+      - const: refclk
 
   iommus:
     maxItems: 1