fpga: disable KUnit test suites when module support is enabled

The fpga core currently assumes that all manager, bridge, and region
devices have a parent device associated with a driver that can be used
to take the module's refcount. This behavior causes the fpga test suites
to crash with a null-ptr-deref since parent fake devices do not have a
driver. This patch disables all fpga KUnit test suites when loadable
module support is enabled until the fpga core is fixed. Test suites
can still be run using the KUnit default UML kernel.

Signed-off-by: Marco Pagani <marpagan@redhat.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Fixes: ccbc1c30

 ("fpga: add an initial KUnit suite for the FPGA Manager")
Link: https://lore.kernel.org/r/20231018163814.100803-1-marpagan@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>