arm: dt: zynq: Add support for the zed platform

Add a DT fragment for the Zed Zynq platform and a corresponding
target to the Makefile

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Reviewed-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>