powerpc/t4240emu: Add device tree file for t4240emu

T4240EMU is an emulator target with minimum peripherals. It is based on
T4240QDS and trimmed down most peripherals due to either not modeled or
lack of board level connections. The main purpose of this minimum dts is
to speed up booting on emulator.

Signed-off-by: York Sun <yorksun@freescale.com>
[scottwood@freescale.com: whitespace fixes]
Signed-off-by: Scott Wood <scottwood@freescale.com>