arm: mvebu: helios4: add MMC to SPL DT

This allows SPL to load the main U-Boot image from MMC once DM_MMC is
enabled.

Signed-off-by: Dennis Gilmore <dennis@ausil.us>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/arch/arm/dts/armada-388-helios4-u-boot.dtsi b/arch/arm/dts/armada-388-helios4-u-boot.dtsi
index 4b20610..f0da9f4 100644
--- a/arch/arm/dts/armada-388-helios4-u-boot.dtsi
+++ b/arch/arm/dts/armada-388-helios4-u-boot.dtsi
@@ -20,3 +20,7 @@
 	status = "okay";
 	u-boot,dm-spl;
 };
+
+&sdhci {
+       u-boot,dm-spl;
+};