ARM: dts: omap3-igep0020: Specify IGEPv2 revision in device tree.

We'll introduce new hardware revisions soon. This patch is only to
indicate which board revision supports this device tree file in order
to avoid confusions.

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>