gpio: reg: Add missing header(s)

Do not imply that some of the generic headers may be always included.
Instead, include explicitly what we are direct user of.

While at it, split out the GPIO group of headers.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpio-reg.c

@@ -4,11 +4,19 @@
  *
  * Copyright (C) 2016 Russell King
  */
-#include <linux/gpio/driver.h>
-#include <linux/gpio/gpio-reg.h>
+#include <linux/bits.h>
+#include <linux/container_of.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/errno.h>
 #include <linux/io.h>
+#include <linux/irqdomain.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/types.h>
+
+#include <linux/gpio/driver.h>
+#include <linux/gpio/gpio-reg.h>
 
 struct gpio_reg {
 	struct gpio_chip gc;