configs: rk3399: enable rng on firefly/rock960/rockpro64

Enable the RNG on the Firefly, rock960 and RockPro64 devices
to enable KASLR on devices that support it.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Cc: Akash Gajjar <akash@openedev.com>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Kever Yang <kever.yang@rock-chips.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Kever Yang<kever.yang@rock-chips.com>
diff --git a/configs/firefly-rk3399_defconfig b/configs/firefly-rk3399_defconfig
index c453b82..cfbaae4 100644
--- a/configs/firefly-rk3399_defconfig
+++ b/configs/firefly-rk3399_defconfig
@@ -35,6 +35,8 @@
 CONFIG_MMC_DW_ROCKCHIP=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_ROCKCHIP=y
+CONFIG_DM_RNG=y
+CONFIG_RNG_ROCKCHIP=y
 CONFIG_SF_DEFAULT_SPEED=20000000
 CONFIG_DM_ETH=y
 CONFIG_ETH_DESIGNWARE=y