x86/kasan: Add message about KASAN being initialized

Print informational message to tell user that kernel
runs with KASAN enabled.

Add a "kasan: " prefix to all messages in kasan_init_64.c.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Alexander Popov <alpopov@ptsecurity.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <adech.fo@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1435828178-10975-6-git-send-email-a.ryabinin@samsung.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/kasan_init_64.c

+#define pr_fmt(fmt) "kasan: " fmt
 #include <linux/bootmem.h>
 #include <linux/kasan.h>
 #include <linux/kdebug.h>
@@ -237,4 +238,6 @@ void __init kasan_init(void)
 	load_cr3(init_level4_pgt);
 	__flush_tlb_all();
 	init_task.kasan_depth = 0;
+
+	pr_info("Kernel address sanitizer initialized\n");
 }