mfd: simple-mfd-i2c: Don't use "proxy" headers

Update header inclusions to follow IWYU (Include What You Use) principle.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/simple-mfd-i2c.c

···
  * will be subsequently registered.
  */
 
+#include <linux/array_size.h>
+#include <linux/dev_printk.h>
+#include <linux/err.h>
 #include <linux/i2c.h>
-#include <linux/kernel.h>
 #include <linux/mfd/core.h>
+#include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
 #include <linux/regmap.h>
+#include <linux/stddef.h>
 
 #include "simple-mfd-i2c.h"