gpiolib: add missing declarations

Add declaration of 'struct of_phandle_args' to avoid the following
warning:

  In file included from arch/arm/mach-tegra/board-paz00.c:21:0:
  include/linux/gpio/driver.h:102:17: warning: 'struct of_phandle_args' declared inside parameter list
  include/linux/gpio/driver.h:102:17: warning: its scope is only this definition or declaration, which is probably not what you want

Also proactively add other definitions/includes that could be missing
in other contexts.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reported-by: Stephen Warren <swarren@wwwdotorg.org>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -2,9 +2,12 @@
 #define __LINUX_GPIO_DRIVER_H
 
 #include <linux/types.h>
+#include <linux/module.h>
 
 struct device;
 struct gpio_desc;
+struct of_phandle_args;
+struct device_node;
 struct seq_file;
 
 /**