null_blk: Add rotational feature support

To facilitate testing of kernel functions related to the rotational
feature (BLK_FEAT_ROTATIONAL) of a block device (e.g. NVMe rotational
bit support), add the rotational boolean configfs attribute and module
parameter to the null_blk driver. If set, a null block device will
report being a rotational device through it queue limits features with
the BLK_FEAT_ROTATIONAL flag.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20241126000956.95983-1-dlemoal@kernel.org


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