staging: fpga: Adding FPGA Manager support for Xilinx Zynq

This commit adds FPGA Manager support for the Xilinx Zynq chip.
The code heavily borrows from the xdevcfg driver in Xilinx'
vendor tree.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>