mm/damon/{dbgfs,sysfs}: move target_has_pid() from dbgfs to damon.h

mm/damon/{dbgfs,sysfs}: move target_has_pid() from dbgfs to damon.h

The function for knowing if given monitoring context's targets will have
pid or not is defined and used in dbgfs only.  However, the logic is also
needed for sysfs.  This commit moves the code to damon.h and makes both
dbgfs and sysfs to use it.

Link: https://lkml.kernel.org/r/20220606182310.48781-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>