ARM: dts: N900: Add device tree

This adds device tree with necessary support to boot with functional
video (on both emulator and real N900 device).

Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>