md: prepare for enable raid1 io serialization

1. The related resources (spin_lock, list and waitqueue) are needed for
address raid1 reorder overlap issue too, in this case, rdev is set to
NULL for mddev_create/destroy_serial_pool which implies all rdevs need
to handle these resources.

And also add "is_suspend" to mddev_destroy_serial_pool since it will
be called under suspended situation, which also makes both create and
destroy pool have same arguments.

2. Introduce rdevs_init_serial which is called if raid1 io serialization
is enabled since all rdevs need to init related stuffs.

3. rdev_init_serial and clear_bit(CollisionCheck, &rdev->flags) should
be called between suspend and resume.

No need to export mddev_create_serial_pool since it is only called in
md-mod module.

Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>