Kynetics has developed and upstreamed support in the meta-sunxi OpenEmbedded layer for the Olimex A20 OLinuXIno LIME2 eMMC, the first Olimex board based on the Allwinner A20 SOC to feature eMMC storage. In particular, the patches add support for the eMMC in U-Boot and the Linux kernel including automatic selection of boot partitions based on the storage which U-Boot has been loaded from.
You can find the patches on Github.