block: move the raid_partial_stripes_expensive flag into the features field

Move the raid_partial_stripes_expensive flags into the features field to
reclaim a little bit of space.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20240619154623.450048-7-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>