Thanks to an additional U-Boot patch from Carlo Caione, it is now possible to (partially) boot the mainline Kernel from U-Boot on an eMMC module, as well as from SDcard..    Patch details here:  https://www.mail-archive.com/u-boot@lists.denx.de/msg213468.html

=> mmc info
Device: <NULL>
Manufacturer ID: 15
OEM: 100
Name: BGND3
Tran Speed: 52000000
Rd Block Len: 512
MMC version 5.0
High Capacity: Yes
Capacity: 29.1 GiB
Bus Width: 8-bit
Erase Group Size: 512 KiB
HC WP Group Size: 8 MiB
User Capacity: 29.1 GiB WRREL
Boot Capacity: 4 MiB ENH
RPMB Capacity: 4 MiB ENH
=>
=> mmc part
Partition Map for MMC device 0 -- Partition Type: DOS
Part Start Sector Num Sectors UUID         Type
 1   2048         56973312    d3630000-01   83
 2   56975360     4096000     d3630000-02   82

As I mentioned in an earlier article, it is not -yet – possible to boot the Kernel all the way from MMC devices, as support is not in the current (May 22) version of Linux-Next..

Robert Gadsdon.    May 22, 2016.