ARM: ux500: Add skeleton DTS file for the u9540

This patch sees the creation of a sparse Device Tree file for
ST-Ericsson's latest development board supporting the latest
dual-core Cortex-a9 u9540 SoC.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>