ARM: dts: Add devicetree for gta04 board.

This adds devicetree for gta04 (Openmoko next generation board) with necessary
support for mmc, usb, leds and button.

Signed-off-by: Marek Belisko <marek@goldelico.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>