[S390] Move psw_set_key.

Move psw_set_key() from ptrace.h to processor.h which is a more
suitable place for it. In addition the moves makes the function
invisible to user space.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

include/asm-s390/processor.h

@@ -216,6 +216,11 @@ static inline void cpu_relax(void)
 	barrier();
 }
 
+static inline void psw_set_key(unsigned int key)
+{
+	asm volatile("spka 0(%0)" : : "d" (key));
+}
+
 /*
  * Set PSW to specified value.
  */