xtensa: add power management menu to Kconfig

This allows using runtime power management feature on Xtensa.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 81f57e8..697fb28 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -414,6 +414,12 @@
 
 endmenu
 
+menu "Power management options"
+
+source "kernel/power/Kconfig"
+
+endmenu
+
 source "net/Kconfig"
 
 source "drivers/Kconfig"