[AVR32] ratelimit segfault reporting rate

Limit the rate of the kernel logging for the segfaults of user
applications, to avoid potential message floods or denial-of-service
attacks.
Signed-off-by: Andrea Righi <a.righi@cineca.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/mm/fault.c

@@ -158,7 +158,7 @@ asmlinkage void do_page_fault(unsigned long ecr, struct pt_regs *regs)
 	up_read(&mm->mmap_sem);
 
 	if (user_mode(regs)) {
-		if (exception_trace)
+		if (exception_trace && printk_ratelimit())
 			printk("%s%s[%d]: segfault at %08lx pc %08lx "
 			       "sp %08lx ecr %lu\n",
 			       is_init(tsk) ? KERN_EMERG : KERN_INFO,