imx6: icorem6: Add NAND support

Add NAND support for Engicam i.CoreM6 qdl board.

Boot Log:
--------

U-Boot SPL 2016.09-rc2-30755-gd3dc581-dirty (Sep 28 2016 - 23:00:43)
Trying to boot from NAND
NAND : 512 MiB

U-Boot 2016.09-rc2-30755-gd3dc581-dirty (Sep 28 2016 - 23:00:43 +0530)

CPU:   Freescale i.MX6SOLO rev1.3 at 792MHz
CPU:   Industrial temperature grade (-40C to 105C) at 55C
Reset cause: WDOG
Model: Engicam i.CoreM6 DualLite/Solo Starter Kit
DRAM:  256 MiB
NAND:  512 MiB
MMC:   FSL_SDHC: 0
In:    serial
Out:   serial
Err:   serial
Net:   FEC [PRIME]
Hit any key to stop autoboot:  0
icorem6qdl>

Cc: Scott Wood <oss@buserror.net>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>