kernel.h: Move ARRAY_SIZE() to a separate header

Touching files so used for the kernel,
forces 'make' to recompile most of the kernel.

Having those definitions in more granular files
helps avoid recompiling so much of the kernel.

Signed-off-by: Alejandro Colomar <alx@kernel.org>
Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20230817143352.132583-2-lucas.segarra.fernandez@intel.com
[andy: reduced to cover only string.h for now]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

include/linux/kernel.h

@@ -13,6 +13,7 @@
 
 #include <linux/stdarg.h>
 #include <linux/align.h>
+#include <linux/array_size.h>
 #include <linux/limits.h>
 #include <linux/linkage.h>
 #include <linux/stddef.h>
@@ -50,12 +51,6 @@
 #define READ			0
 #define WRITE			1
 
-/**
- * ARRAY_SIZE - get the number of elements in array @arr
- * @arr: array to be sized
- */
-#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
-
 #define PTR_IF(cond, ptr)	((cond) ? (ptr) : NULL)
 
 #define u64_to_user_ptr(x) (		\