powerpc/b4860emu: Add device tree file for b4860emu

B4860EMU is a emualtor target with minimum peripherals. It is based on
B4860QDS 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 fix]
Signed-off-by: Scott Wood <scottwood@freescale.com>