Hi Alexandre,
To use our (the Boundary Devices) Android, the SD card creation process uses device/boundary/mksdcard.sh, not the steps described in the Freescale docs.
Also, the U-Boot build is completely independent thing and U-Boot doesn't live on SD card. Instead, it resides in SPI-NOR.
SergioSolis, our boards don't use u-boot-6q.bin. We use main-line U-Boot, so the output of a build is in u-boot.imx.
More details are available in this page:
http://boundarydevices.com/u-boot-on-i-mx6/
The latest U-Boot binaries are in this page (U-Boot 2014.04) and they don't support MFG tool:
http://boundarydevices.com/u-boot-2014-04-release-mx6/
The file u-boot.nitrogen6q is the one for use on SABRE Lite (it does auto-detection of SABRE Lite/Nitrogen6x) and you can update it using the "upgradeu" command by extracting the tar-ball in the release page to a single-partition SD card like so:
U-Boot > bootfile=u-boot.nitrogen6q ; run upgradeu