gpio: mmio: Clean up headers

There is a few things done:
- include only the headers we are direct user of
- add missing headers
- group generic headers and subsystem headers
- sort each group alphabetically

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/gpio-mmio.c

@@ -40,24 +40,22 @@ o        `                     ~~~~\___/~~~~    ` controller in FPGA is ,.`
  *               `.......````.```
  */
 
-#include <linux/init.h>
+#include <linux/bitops.h>
+#include <linux/compiler.h>
 #include <linux/err.h>
-#include <linux/bug.h>
-#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+#include <linux/log2.h>
+#include <linux/mod_devicetable.h>
 #include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
 #include <linux/spinlock.h>
-#include <linux/compiler.h>
 #include <linux/types.h>
-#include <linux/errno.h>
-#include <linux/log2.h>
-#include <linux/ioport.h>
-#include <linux/io.h>
+
 #include <linux/gpio/driver.h>
-#include <linux/slab.h>
-#include <linux/bitops.h>
-#include <linux/platform_device.h>
-#include <linux/property.h>
-#include <linux/mod_devicetable.h>
 
 #include "gpiolib.h"