arch/tile: implement panic_smp_self_stop()

This allows the later-panicking tiles to wait in a lower power state
until they get interrupted with an smp_send_stop().
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/smp.c

@@ -113,6 +113,12 @@ void smp_send_stop(void)
 	send_IPI_allbutself(MSG_TAG_STOP_CPU);
 }
 
+/* On panic, just wait; we may get an smp_send_stop() later on. */
+void panic_smp_self_stop(void)
+{
+	while (1)
+		asm("nap; nop");
+}
 
 /*
  * Dispatch code called from hv_message_intr() for HV_MSG_TILE hv messages.