[S390] Use diagnose 308 for system reset

The diagnose 308 call is the prefered method for clearing all ongoing I/O.
Therefore if it is available we use it instead of doing a manual reset.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/kernel/ipl.c

@@ -1996,6 +1996,12 @@ static void do_reset_calls(void)
 {
 	struct reset_call *reset;
 
+#ifdef CONFIG_64BIT
+	if (diag308_set_works) {
+		diag308_reset();
+		return;
+	}
+#endif
 	list_for_each_entry(reset, &rcall, list)
 		reset->fn();
 }