rockchip: rk3399: Migrate to use common spl board file

rk3399 has similar boot flow in SPL with other Rockchip SoCs,
migrate to use common spl board file.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index 25214bc..81dee9e 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -170,6 +170,7 @@
 	select DM_PMIC
 	select DM_REGULATOR_FIXED
 	select BOARD_LATE_INIT
+	imply SPL_ROCKCHIP_COMMON_BOARD
 	imply TPL_SERIAL_SUPPORT
 	imply TPL_LIBCOMMON_SUPPORT
 	imply TPL_LIBGENERIC_SUPPORT