sched,freezer: Mark TASK_FROZEN special

The special task states are those that do not suffer spurious wakeups,
TASK_FROZEN is very much one of those, mark it as such.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105029.998329901@infradead.org