gpio: samsung: add flags specifier to device-tree binding

This adds a flags field to the gpio specifier for Samsung. I didn't
want to add yet another field in the already quite long specifier, so
I decided to compress it together with the Pull Up/Down settings instead.

This is needed to, for example, have a gpio-keys input that is active low.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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

@@ -11,14 +11,15 @@ Required properties:
      <[phandle of the gpio controller node]
       [pin number within the gpio controller]
       [mux function]
-      [pull up/down]
+      [flags and pull up/down]
       [drive strength]>
 
   Values for gpio specifier:
   - Pin number: is a value between 0 to 7.
-  - Pull Up/Down: 0 - Pull Up/Down Disabled.
+  - Flags and Pull Up/Down: 0 - Pull Up/Down Disabled.
                             1 - Pull Down Enabled.
                             3 - Pull Up Enabled.
+          Bit 16 (0x00010000) - Input is active low.
   - Drive Strength: 0 - 1x,
                     1 - 3x,
                     2 - 2x,

drivers/gpio/gpio-samsung.c

@@ -2681,11 +2681,14 @@ static int exynos_gpio_xlate(struct gpio_chip *gc,
 
 	if (s3c_gpio_cfgpin(pin, S3C_GPIO_SFN(gpiospec->args[1])))
 		pr_warn("gpio_xlate: failed to set pin function\n");
-	if (s3c_gpio_setpull(pin, gpiospec->args[2]))
+	if (s3c_gpio_setpull(pin, gpiospec->args[2] & 0xffff))
 		pr_warn("gpio_xlate: failed to set pin pull up/down\n");
 	if (s5p_gpio_set_drvstr(pin, gpiospec->args[3]))
 		pr_warn("gpio_xlate: failed to set pin drive strength\n");
 
+	if (flags)
+		*flags = gpiospec->args[2] >> 16;
+
 	return gpiospec->args[0];
 }