ARM: dts: omap3-igep0020: Add NAND flash support

The IGEPv2 board has an 512MB NAND flash memory.

Add a device node for this NAND and its partition layout.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>