mfd: syscon: atmel-smc: Don't use "proxy" headers

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

Note that kernel.h is discouraged to be included as it's written
at the top of that file.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/atmel-smc.c

···
  * Author: Boris Brezillon <[e-mail]>
  */
 
-#include <linux/mfd/syscon/atmel-smc.h>
+#include <linux/bits.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/mod_devicetable.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
 #include <linux/string.h>
+
+#include <linux/mfd/syscon/atmel-smc.h>
 
 /**
  * atmel_smc_cs_conf_init - initialize a SMC CS conf

include/linux/mfd/syscon/atmel-smc.h

···
 #ifndef _LINUX_MFD_SYSCON_ATMEL_SMC_H_
 #define _LINUX_MFD_SYSCON_ATMEL_SMC_H_
 
-#include <linux/kernel.h>
-#include <linux/of.h>
-#include <linux/regmap.h>
+#include <linux/bits.h>
+#include <linux/types.h>
+
+struct device_node;
+struct regmap;
 
 #define ATMEL_SMC_SETUP(cs)			(((cs) * 0x10))
 #define ATMEL_HSMC_SETUP(layout, cs)		\