kernel: fix smp build on esp32

set_kernel_idle_time_in_ticks is not used in non SMP code.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/kernel/idle.c b/kernel/idle.c
index 036bacf..8ff5b82 100644
--- a/kernel/idle.c
+++ b/kernel/idle.c
@@ -51,6 +51,7 @@
  *
  * @return N/A
  */
+#ifndef CONFIG_SMP
 static void set_kernel_idle_time_in_ticks(s32_t ticks)
 {
 #ifdef CONFIG_SYS_POWER_MANAGEMENT
@@ -58,7 +59,6 @@
 #endif
 }
 
-#ifndef CONFIG_SMP
 static void sys_power_save_idle(void)
 {
 	s32_t ticks = _get_next_timeout_expiry();