mx28evk: Add documentation on how to boot from SPI NOR

Explain the necessary steps in order to boot from SPI NOR.

Based on a earlier submission from Mårten Wikman.

Signed-off-by: Mårten Wikman <marten.wikman@novia.fi>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
2 files changed