gpio: mpc8xxx: Add new platforms GPIO DT node description

Update the NXP GPIO node dt-binding file for QorIQ and
Layerscape platforms, and add one more example with
ls1028a GPIO node.
Signed-off-by: Song Hui <hui.song_1@nxp.com>
Link: https://lore.kernel.org/r/20190807021254.49092-1-hui.song_1@nxp.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-mpc8xxx.txt

@@ -4,7 +4,7 @@ Required properties:
 - compatible : Should be "fsl,<soc>-gpio"
   The following <soc>s are known to be supported:
 	mpc5121, mpc5125, mpc8349, mpc8572, mpc8610, pq3, qoriq,
-	ls1021a, ls1043a, ls2080a.
+	ls1021a, ls1043a, ls2080a, ls1028a.
 - reg : Address and length of the register set for the device
 - interrupts : Should be the port interrupt shared by all 32 pins.
 - #gpio-cells : Should be two.  The first cell is the pin number and
@@ -37,3 +37,17 @@ gpio0: gpio@2300000 {
 	interrupt-controller;
 	#interrupt-cells = <2>;
 };
+
+
+Example of gpio-controller node for a ls1028a SoC:
+
+gpio1: gpio@2300000 {
+	compatible = "fsl,ls1028a-gpio","fsl,qoriq-gpio";
+	reg = <0x0 0x2300000 0x0 0x10000>;
+	interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
+	gpio-controller;
+	#gpio-cells = <2>;
+	interrupt-controller;
+	#interrupt-cells = <2>;
+	little-endian;
+};