staging: xillybus: Removed force to be a module

The driver was forced to "module only" following a previous failure to build
into the kernel. The problem was resolved several months ago.

This has been successfully tested with "make allyesconfig" on x86_64.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>