mx28: Split the README into a common part and a m28 specific part

Split the README into a common part and a m28 specific part.

This will make things easier when adding new README files for other mx28
based boards.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
2 files changed