dt-bindings: net: bcm4908-enet: add optional TX interrupt

I discovered that hardware actually supports two interrupts, one per DMA
channel (RX and TX).
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/brcm,bcm4908-enet.yaml

@@ -22,10 +22,18 @@ properties:
     maxItems: 1
 
   interrupts:
-    description: RX interrupt
+    minItems: 1
+    maxItems: 2
+    items:
+      - description: RX interrupt
+      - description: TX interrupt
 
   interrupt-names:
-    const: rx
+    minItems: 1
+    maxItems: 2
+    items:
+      - const: rx
+      - const: tx
 
 required:
   - reg
@@ -43,6 +51,7 @@ examples:
         compatible = "brcm,bcm4908-enet";
         reg = <0x80002000 0x1000>;
 
-        interrupts = <GIC_SPI 86 IRQ_TYPE_LEVEL_HIGH>;
-        interrupt-names = "rx";
+        interrupts = <GIC_SPI 86 IRQ_TYPE_LEVEL_HIGH>,
+                     <GIC_SPI 87 IRQ_TYPE_LEVEL_HIGH>;
+        interrupt-names = "rx", "tx";
     };