[S390] add kprobes annotations

Add kprobes annotations to get the massive 'probe kernel.function("*") {}'
stress test working.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index dfe015d..4a6e1a5 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -7,6 +7,8 @@
 
 #include <asm/asm-offsets.h>
 
+	.section .kprobes.text, "ax"
+
 	.globl ftrace_stub
 ftrace_stub:
 	br	%r14