arm: zynq: Add Xilinx cc108 board

The board contains 7z010 with 512MB memory, ethernet, qspi, uart, usbs
and sd. But board is not supporting booting from sd card.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Rob Herring <robh@kernel.org>