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 <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250627164414.1043434-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: andy-shev

drivers/mfd/atmel-smc.c

@@ -8,9 +8,16 @@
  * Author: Boris Brezillon <boris.brezillon@free-electrons.com>
  */
 
-#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
  * @conf: the SMC CS conf to initialize

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

@@ -11,9 +11,11 @@
 #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)		\