configs: rockpro64: Enable LPDDR4 support

Due to foot-print issues, we have LPDDR4 code can be
marked as CONFIG_RAM_RK3399_LPDDR4.

So, enable it for Rockpro64 board.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <Kever.yang@rock-chips.com>
diff --git a/configs/rockpro64-rk3399_defconfig b/configs/rockpro64-rk3399_defconfig
index e8fc7ae..39e68aa 100644
--- a/configs/rockpro64-rk3399_defconfig
+++ b/configs/rockpro64-rk3399_defconfig
@@ -28,6 +28,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="rk3399-rockpro64"
 CONFIG_OF_SPL_REMOVE_PROPS="pinctrl-0 pinctrl-names clock-names interrupt-parent assigned-clocks assigned-clock-rates assigned-clock-parents"
 CONFIG_ENV_IS_IN_MMC=y
+CONFIG_RAM_RK3399_LPDDR4=y
 CONFIG_ROCKCHIP_GPIO=y
 CONFIG_SYS_I2C_ROCKCHIP=y
 CONFIG_MMC_DW=y