rockchip: arm64: rk3399: add SPL support

Add SPL support for rk3399, default with of-platdata enabled.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Drop Kconfig changes to fix build error:
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-rockchip/Makefile b/arch/arm/mach-rockchip/Makefile
index 7b8abc2..151fa2d 100644
--- a/arch/arm/mach-rockchip/Makefile
+++ b/arch/arm/mach-rockchip/Makefile
@@ -11,6 +11,7 @@
 obj-$(CONFIG_ROCKCHIP_RK3036) += rk3036-board-spl.o
 obj-$(CONFIG_ROCKCHIP_RK3188) += rk3188-board-spl.o
 obj-$(CONFIG_ROCKCHIP_RK3288) += rk3288-board-spl.o
+obj-$(CONFIG_ROCKCHIP_RK3399) += rk3399-board-spl.o
 obj-$(CONFIG_ROCKCHIP_BROM_HELPER) += save_boot_param.o
 else
 obj-$(CONFIG_ROCKCHIP_RK3188) += rk3188-board.o