ARM: mx28evk: Add SPI flash support

mx28evk has a free slot (J89) which can be used to populate an SPI NOR Flash.

Add support for it.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>