ARM: dts: Add basic device tree support for omap2430 sdp

I doubt that there are many people using 2430 sdp, but as
that's been historically an important acid test platform
for omap2+ related changes, let's add minimal device
tree support for it.

If anybody is using it beyond minimal boot testing, patches
for more complete device tree support are welcome.

Cc: devicetree@vger.kernel.org
Cc: "Benoît Cousson" <bcousson@baylibre.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>