ARM: dts: overo: Support PoP NAND

Some Overo COM models include NAND flash in the on-board
package-on-package (PoP) chip.  Add this to the base Overo devicetree.

Most commonly, this is 512MB NAND from the Micron MT29C4G96MAZ family
but, as discussed [1], several different sized are possible. To
support different sizes, the last partition should fill to the end of
the chip (i.e. MTDPART_SIZ_FULL).

With thanks to Florian Vaussard for the original patch [2] and Adam Lee for
updating it here.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2013-June/175760.html
[2] http://lists.infradead.org/pipermail/linux-arm-kernel/2013-June/175449.html

Signed-off-by: Ash Charles <ashcharles@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>