config: Add defconfig for Freescale i.MX28 EVK

The i.MX28 Evaluation Kit (or EVK) is Freescale's evaluation board based on the
i.MX287 Applications Processor.

This defconfig is based on mainline u-boot and Linux kernel.

Also, we add an SD card creation script and documentation, shamelessly based on
the ones for i.MX5/6 by Luca Ceresoli.

[Arnout: fixate U-Boot and kernel (headers) versions]

Signed-off-by: Vincent Stehlé <vincent.stehle@freescale.com>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>