rockchip: rk3399: Enable DT overlay support on all boards

Imply OF_LIBFDT_OVERLAY Kconfig options to add device tree overlay
support on all RK3399 boards.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index 6f1213b..bfde9bf 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -269,6 +269,7 @@
 	imply LEGACY_IMAGE_FORMAT
 	imply MISC
 	imply MISC_INIT_R
+	imply OF_LIBFDT_OVERLAY
 	imply OF_LIVE
 	imply PARTITION_TYPE_GUID
 	imply PHY_GIGE if GMAC_ROCKCHIP