gpio: Avoid kernel.h inclusion where it's possible

Inclusion of kernel.h increases the mess with the header dependencies.
Avoid kernel.h inclusion where it's possible.

Besides that, clean up a bit other inclusions inside GPIO subsystem headers.
It includes:
 - removal pin control bits (forward declaration and header) from linux/gpio.h
 - removal of.h from asm-generic/gpio.h
 - use of explicit headers in gpio/consumer.h
 - add FIXME note with regard to gpio.h inclusion in of_gpio,h
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200205134336.20197-1-andriy.shevchenko@linux.intel.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

include/asm-generic/gpio.h

@@ -2,10 +2,8 @@
 #ifndef _ASM_GENERIC_GPIO_H
 #define _ASM_GENERIC_GPIO_H
 
-#include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/errno.h>
-#include <linux/of.h>
 
 #ifdef CONFIG_GPIOLIB
 
@@ -140,6 +138,8 @@ static inline void gpio_unexport(unsigned gpio)
 
 #else	/* !CONFIG_GPIOLIB */
 
+#include <linux/kernel.h>
+
 static inline bool gpio_is_valid(int number)
 {
 	/* only non-negative numbers are valid */

include/linux/gpio.h

@@ -102,11 +102,9 @@ void devm_gpio_free(struct device *dev, unsigned int gpio);
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/bug.h>
-#include <linux/pinctrl/pinctrl.h>
 
 struct device;
 struct gpio_chip;
-struct pinctrl_dev;
 
 static inline bool gpio_is_valid(int number)
 {

include/linux/gpio/consumer.h

@@ -2,9 +2,10 @@
 #ifndef __LINUX_GPIO_CONSUMER_H
 #define __LINUX_GPIO_CONSUMER_H
 
+#include <linux/bits.h>
 #include <linux/bug.h>
+#include <linux/compiler_types.h>
 #include <linux/err.h>
-#include <linux/kernel.h>
 
 struct device;
 
@@ -189,6 +190,8 @@ struct gpio_desc *devm_fwnode_gpiod_get_index(struct device *dev,
 
 #else /* CONFIG_GPIOLIB */
 
+#include <linux/kernel.h>
+
 static inline int gpiod_count(struct device *dev, const char *con_id)
 {
 	return 0;

include/linux/of_gpio.h

@@ -11,9 +11,8 @@
 #define __LINUX_OF_GPIO_H
 
 #include <linux/compiler.h>
-#include <linux/kernel.h>
-#include <linux/errno.h>
-#include <linux/gpio.h>
+#include <linux/gpio/driver.h>
+#include <linux/gpio.h>		/* FIXME: Shouldn't be here */
 #include <linux/of.h>
 
 struct device_node;
@@ -34,6 +33,8 @@ enum of_gpio_flags {
 
 #ifdef CONFIG_OF_GPIO
 
+#include <linux/kernel.h>
+
 /*
  * OF GPIO chip for memory mapped banks
  */
@@ -63,6 +64,8 @@ extern void of_mm_gpiochip_remove(struct of_mm_gpio_chip *mm_gc);
 
 #else /* CONFIG_OF_GPIO */
 
+#include <linux/errno.h>
+
 /* Drivers may not strictly depend on the GPIO support, so let them link. */
 static inline int of_get_named_gpio_flags(struct device_node *np,
 		const char *list_name, int index, enum of_gpio_flags *flags)