um: Fix the declaration of kasan_map_memory

JIRA: https://issues.redhat.com/browse/RHEL-84184

This patch is a backport of the following upstream commit:
commit 6a85e34
Author: Tiwei Bie <tiwei.btw@antgroup.com>
Date:   Tue Apr 23 20:58:55 2024 +0800

    um: Fix the declaration of kasan_map_memory

    Make it match its definition (size_t vs unsigned long). And declare
    it in a shared header to fix the -Wmissing-prototypes warning, as it
    is defined in the user code and called in the kernel code.

    Fixes: 5b30140 ("UML: add support for KASAN under x86_64")
    Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
    Signed-off-by: Richard Weinberger <richard@nod.at>

Signed-off-by: Rafael Aquini <raquini@redhat.com>

Author: Rafael Aquini

arch/um/include/asm/kasan.h

@@ -24,7 +24,6 @@
 
 #ifdef CONFIG_KASAN
 void kasan_init(void);
-void kasan_map_memory(void *start, unsigned long len);
 extern int kasan_um_is_ready;
 
 #ifdef CONFIG_STATIC_LINK

arch/um/include/shared/kern_util.h

@@ -69,4 +69,6 @@ extern void fatal_sigsegv(void) __attribute__ ((noreturn));
 
 void um_idle_sleep(void);
 
+void kasan_map_memory(void *start, size_t len);
+
 #endif

arch/um/os-Linux/mem.c

@@ -15,6 +15,7 @@
 #include <sys/vfs.h>
 #include <linux/magic.h>
 #include <init.h>
+#include <kern_util.h>
 #include <os.h>
 
 /*