fpga manager: Add hardware dependency to Zynq driver

The Zynq FPGA manager driver serves no purpose on other architectures
so hide it unless build-testing.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Moritz Fischer <moritz.fischer@ettus.com>
Acked-by: Alan Tull <atull@opensource.altera.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Cc: "Sören Brinkmann" <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>