bindings: net: stmmac: add missing note about LPI interrupt

The hardware has a LPI interrupt.
There is already code in the stmmac driver to parse and handle the
interrupt. However, this information was missing from the DT binding.

At the same time, improve the description of the existing interrupts.
Signed-off-by: NNiklas Cassel <niklas.cassel@axis.com>
Acked-By: NJoao Pinto <jpinto@synopsys.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/stmmac.txt

@@ -7,9 +7,12 @@ Required properties:
 - interrupt-parent: Should be the phandle for the interrupt controller
   that services interrupts for this device
 - interrupts: Should contain the STMMAC interrupts
-- interrupt-names: Should contain the interrupt names "macirq"
-  "eth_wake_irq" if this interrupt is supported in the "interrupts"
-  property
+- interrupt-names: Should contain a list of interrupt names corresponding to
+	the interrupts in the interrupts property, if available.
+	Valid interrupt names are:
+  - "macirq" (combined signal for various interrupt events)
+  - "eth_wake_irq" (the interrupt to manage the remote wake-up packet detection)
+  - "eth_lpi" (the interrupt that occurs when Tx or Rx enters/exits LPI state)
 - phy-mode: See ethernet.txt file in the same directory.
 - snps,reset-gpio 	gpio number for phy reset.
 - snps,reset-active-low boolean flag to indicate if phy reset is active low.
@@ -152,8 +155,8 @@ Examples:
 		compatible = "st,spear600-gmac";
 		reg = <0xe0800000 0x8000>;
 		interrupt-parent = <&vic1>;
-		interrupts = <24 23>;
-		interrupt-names = "macirq", "eth_wake_irq";
+		interrupts = <24 23 22>;
+		interrupt-names = "macirq", "eth_wake_irq", "eth_lpi";
 		mac-address = [000000000000]; /* Filled in by U-Boot */
 		max-frame-size = <3800>;
 		phy-mode = "gmii";