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

include/linux/gpio/gpio-reg.h

@@ -2,9 +2,13 @@
 #ifndef GPIO_REG_H
 #define GPIO_REG_H
 
+#include <linux/types.h>
+
 struct device;
 struct irq_domain;
 
+struct gpio_chip;
+
 struct gpio_chip *gpio_reg_init(struct device *dev, void __iomem *reg,
 	int base, int num, const char *label, u32 direction, u32 def_out,
 	const char *const *names, struct irq_domain *irqdom, const int *irqs);