arch/tile: add "nop" after "nap" to help GX idle power draw

This avoids the hardware istream prefetcher doing unnecessary work.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/entry.S

@@ -85,6 +85,7 @@ STD_ENTRY(cpu_idle_on_new_stack)
 /* Loop forever on a nap during SMP boot. */
 STD_ENTRY(smp_nap)
 	nap
+	nop       /* avoid provoking the icache prefetch with a jump */
 	j smp_nap /* we are not architecturally guaranteed not to exit nap */
 	jrp lr    /* clue in the backtracer */
 	STD_ENDPROC(smp_nap)
@@ -105,5 +106,6 @@ STD_ENTRY(_cpu_idle)
 	.global _cpu_idle_nap
 _cpu_idle_nap:
 	nap
+	nop       /* avoid provoking the icache prefetch with a jump */
 	jrp lr
 	STD_ENDPROC(_cpu_idle)

arch/tile/kernel/smp.c

@@ -103,7 +103,7 @@ static void smp_stop_cpu_interrupt(void)
 	set_cpu_online(smp_processor_id(), 0);
 	arch_local_irq_disable_all();
 	for (;;)
-		asm("nap");
+		asm("nap; nop");
 }
 
 /* This function calls the 'stop' function on all other CPUs in the system. */