xtensa: add power management menu to Kconfig

This allows using runtime power management feature on Xtensa.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/Kconfig

@@ -414,6 +414,12 @@ source "fs/Kconfig.binfmt"
 
 endmenu
 
+menu "Power management options"
+
+source "kernel/power/Kconfig"
+
+endmenu
+
 source "net/Kconfig"
 
 source "drivers/Kconfig"