[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>

arch/s390/kernel/entry.S

@@ -188,6 +188,8 @@ STACK_SIZE  = 1 << STACK_SHIFT
 	ssm	__SF_EMPTY(%r15)
 	.endm
 
+	.section .kprobes.text, "ax"
+
 /*
  * Scheduler resume function, called by switch_to
  *  gpr2 = (task_struct *) prev
@@ -861,6 +863,8 @@ restart_crash:
 restart_go:
 #endif
 
+	.section .kprobes.text, "ax"
+
 #ifdef CONFIG_CHECK_STACK
 /*
  * The synchronous or the asynchronous stack overflowed. We are dead.