selftests/filesystems: Don't run dnotify_test by default

In commit ce290a19 ("selftests: add devpts selftests"), the
filesystems directory was added to the top-level selftests Makefile.

That had the effect of causing the existing dnotify_test in the
filesystems directory to now be run as part of the default selftests
test-run. Unfortunately dnotify_test is actually an infinite loop.

Fix it by moving dnotify_test to TEST_GEN_PROGS_EXTENDED, which says
that it's a generated file (ie. built) but should not be run as part
of the default test suite run (it's an "extended" test).

While we're here cleanup a few other things, devpts_pts should be in
TEST_GEN_PROGS to indicate that it's built, and with the above two
changes we no longer need a custom all or clean rule.

Fixes: ce290a19 ("selftests: add devpts selftests")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Christian brauner <christian.brauner@ubuntu.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>