Documentation: dts: xgene: Update interrupt field description

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Keyur Chudgar <kchudgar@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/apm-xgene-enet.txt

@@ -14,7 +14,10 @@ Required properties for all the ethernet interfaces:
   - "enet_csr": Ethernet control and status register address space
   - "ring_csr": Descriptor ring control and status register address space
   - "ring_cmd": Descriptor ring command register address space
-- interrupts: Ethernet main interrupt
+- interrupts: Two interrupt specifiers can be specified.
+  - First is the Rx interrupt.  This irq is mandatory.
+  - Second is the Tx completion interrupt.
+    This is supported only on SGMII based 1GbE and 10GbE interfaces.
 - port-id: Port number (0 or 1)
 - clocks: Reference to the clock entry.
 - local-mac-address: MAC address assigned to this device