Add a genimage.cfg to create a working sdcard.img for the ci20
hardware. We also need a uboot-env.txt to create the partition for
the uboot environment.
Update the board/ci20/readme.txt with the related information. Remove
the tftp netboot description from the readme as it is already to
complicated for a basic bootable example.
Signed-off-by: Johannes Schmitz <johannes.schmitz1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
