sched/completion: Add wait_for_completion_state()

Allows waiting with a custom @state.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20220822114648.922711674@infradead.org