Use deferred actions to simplify the test suite and avoid potential memory
leaks when test cases fail. Remove unnecessary calls to
kunit_device_unregister() since kunit devices are tied to the test context
and released by a deferred action when the test is completed.

Other changes: fix a typo by changing the test suite name to fpga_region in
the kunit_suite struct.
Signed-off-by: Marco Pagani <marpagan@redhat.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20240725125031.308195-4-marpagan@redhat.comSigned-off-by: Xu Yilun <yilun.xu@linux.intel.com>