sched: add macros to define bitops for task atomic flags

sched: add macros to define bitops for task atomic flags

This will simplify code when we add new flags.

v3:
- Kees pointed out that no_new_privs should never be cleared, so we
shouldn't define task_clear_no_new_privs(). we define 3 macros instead
of a single one.

v2:
- updated scripts/tags.sh, suggested by Peter

Cc: Ingo Molnar <[email protected]>
Cc: Miao Xie <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Kees Cook <[email protected]>
Signed-off-by: Zefan Li <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>