of: Add prompt for OF_OVERLAY config

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/Kconfig

@@ -84,7 +84,7 @@ config OF_RESOLVE
 	bool
 
 config OF_OVERLAY
-	bool
+	bool "Device Tree overlays"
 	depends on OF
 	select OF_DYNAMIC
 	select OF_RESOLVE