debugfs: clean up feature test macros with predicate functions

debugfs: clean up feature test macros with predicate functions

Create separate predicate functions to test/set/clear feature flags,
thereby replacing the wordy old macros.  Furthermore, clean out the
places where we open-coded feature tests.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>