ARM: dts: omap3-igep: OneNAND support

Add OneNAND node for IGEP and leave it disabled by default. It is up
to bootloader to enable proper node. Timing just works, but values are
copied over from N900 as I was unable to find chip datasheet.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>