staging: Add Xilinx Clocking Wizard driver

Add a driver for the Xilinx Clocking Wizard soft IP. The clocking wizard
provides an AXI interface to dynamically reconfigure the clocking
resources of Xilinx FPGAs.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>