I directly use code https://github.com/MarvellEmbeddedProcessors/u-boot-marvell with blew modification:
diff --git a/arch/arm/dts/armada-3720-espressobin.dts b/arch/arm/dts/armada-3720-espressobin.dts
index 2ab039c..5922da0 100644
--- a/arch/arm/dts/armada-3720-espressobin.dts
+++ b/arch/arm/dts/armada-3720-espressobin.dts
@@ -118,7 +118,8 @@
marvell,pad-type = "fixed-1-8v";
pinctrl-names = "default";
pinctrl-0 = <&mmc_pins>;
- status = "disabled";
+ #status = "disabled";
+ status = "okay";
#address-cells = <1>;
#size-cells = <0>;
It works well. It would be a bug of armbian build script, since upstream has added support of emmc and dts code changed.