mm: use kstrtobool() instead of strtobool()

strtobool() is the same as kstrtobool().  However, the latter is more used
within the kernel.

In order to remove strtobool() and slightly simplify kstrtox.h, switch to
the other function name.

While at it, include the corresponding header file (<linux/kstrtox.h>)

Link: https://lkml.kernel.org/r/03f9401a6c8b87a1c786a2138d16b048f8d0eb53.1667336095.git.christophe.jaillet@wanadoo.frSigned-off-by: NChristophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: NPasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

mm/page_table_check.c

@@ -4,6 +4,7 @@
  * Copyright (c) 2021, Google LLC.
  * Pasha Tatashin <pasha.tatashin@soleen.com>
  */
+#include <linux/kstrtox.h>
 #include <linux/mm.h>
 #include <linux/page_table_check.h>
 
@@ -23,7 +24,7 @@ EXPORT_SYMBOL(page_table_check_disabled);
 
 static int __init early_page_table_check_param(char *buf)
 {
-	return strtobool(buf, &__page_table_check_enabled);
+	return kstrtobool(buf, &__page_table_check_enabled);
 }
 
 early_param("page_table_check", early_page_table_check_param);

mm/usercopy.c

@@ -12,6 +12,7 @@
 
 #include <linux/mm.h>
 #include <linux/highmem.h>
+#include <linux/kstrtox.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/sched/task.h>
@@ -258,7 +259,7 @@ static bool enable_checks __initdata = true;
 
 static int __init parse_hardened_usercopy(char *str)
 {
-	if (strtobool(str, &enable_checks))
+	if (kstrtobool(str, &enable_checks))
 		pr_warn("Invalid option string for hardened_usercopy: '%s'\n",
 			str);
 	return 1;