xilinx: zynqmp: Check that DT is 64bit aligned

DT needs to be 64bit aligned. If it is not fdt64_to_cpu will fail when try
to read information about reserved memory. The system ends in exception
without any clue what's going it. That's why detect not aligned DT and
panic to show where the issue is coming from.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>