arm: dts: imx6ull-14x14-evk-u-boot: add rngb

Linux microPlatform uses an rngb device in optee-os in boot scheme
SPL -> OPTEE -> U-Boot. To make rngb available for optee-os, enable
it in SPL.

Signed-off-by: Ricardo Salveti <ricardo@foundries.io>
Co-developed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
diff --git a/arch/arm/dts/imx6ull-14x14-evk-u-boot.dtsi b/arch/arm/dts/imx6ull-14x14-evk-u-boot.dtsi
index a6c2cc8..0b18571 100644
--- a/arch/arm/dts/imx6ull-14x14-evk-u-boot.dtsi
+++ b/arch/arm/dts/imx6ull-14x14-evk-u-boot.dtsi
@@ -6,3 +6,7 @@
 &pinctrl_uart1 {
 	bootph-all;
 };
+
+&rngb {
+	bootph-all;
+};