gpio: 74x164: add dt support for nxp's 74x594

The chip is also an 8 bit shift register which works out of the box as a GPO
expander with this patch
Signed-off-by: Nicolas Saenz Julienne <nicolassaenzj@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-74x164.txt

 * Generic 8-bits shift register GPIO driver
 
 Required properties:
-- compatible : Should be "fairchild,74hc595"
+- compatible: Should contain one of the following:
+    "fairchild,74hc595"
+    "nxp,74lvc594"
 - reg : chip select number
 - gpio-controller : Marks the device node as a gpio controller.
 - #gpio-cells : Should be two.  The first cell is the pin number and

drivers/gpio/gpio-74x164.c

@@ -177,6 +177,7 @@ static int gen_74x164_remove(struct spi_device *spi)
 
 static const struct of_device_id gen_74x164_dt_ids[] = {
 	{ .compatible = "fairchild,74hc595" },
+	{ .compatible = "nxp,74lvc594" },
 	{},
 };
 MODULE_DEVICE_TABLE(of, gen_74x164_dt_ids);