fpga: tests: use KUnit devices instead of platform devices

KUnit now provides helper functions to create fake devices, so use them
instead of relying on platform devices.

Other changes: remove an unnecessary white space in the fpga region suite.

Reviewed-by: Russ Weight <russ.weight@linux.dev>
Signed-off-by: Marco Pagani <marpagan@redhat.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20240329174849.248243-1-marpagan@redhat.com


Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>