spl: nand: add support for mxs nand

This utilizes existing mxs_nand support layer to provide a method to load an
image off nand for SPL. The flash device will be detected in order to support
multiple flash devices instead of having layout hard coded at build time.

Cc: Stefan Roese <sr@denx.de>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Andy Ng <andreas2025@gmail.com>
Cc: Eric Nelson <eric.nelson@boundarydevices.com>
Cc: Tapani Utriainen <tapani@technexion.com>
Cc: Tom Rini <trini@ti.com>
Cc: Scott Wood <scottwood@freescale.com>

Signed-off-by: Tim Harvey <tharvey@gateworks.com>