ARM: dts: zynq: Add Parallella device tree

This allows to boot the Adapteva Parallella board to serial console.

Cc: Andreas Olofsson <andreas@adapteva.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>