mm/damon/dbgfs-test: skip dbgfs_set_targets() test if PADDR is not registered

mm/damon/dbgfs-test: skip dbgfs_set_targets() test if PADDR is not registered

The test depends on registration of DAMON_OPS_PADDR.  It would be
registered only when CONFIG_DAMON_PADDR is set.  DAMON core kunit tests do
fake ops registration for such case.  However, the functions for such fake
ops registration is not available to DAMON debugfs interface.  Just skip
the test in the case.

Link: https://lkml.kernel.org/r/20240827030336.7930-7-sj@kernel.org
Fixes: 999b9467974f ("mm/damon/dbgfs-test: fix is_target_id() change")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>