staging: New driver: Xillybus generic interface for FPGA

This is the driver for Xillybus, which is a general-purpose interface for
data communication with FPGAs (programmable logic). Please refer to the
README included in this patch for a detailed explanation.

It was previously submitted for misc-devices, but it appears like noone's
willing to review the code (which I can understand, given its magnitude).
Hence submitted as a staging driver.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>