block: move q->sysfs_lock and queue-freeze under show/store method

block: move q->sysfs_lock and queue-freeze under show/store method

In preparation to further simplify and group sysfs attributes which
don't require locking or require some form of locking other than q->
limits_lock, move acquire/release of q->sysfs_lock and queue freeze/
unfreeze under each attributes' respective show/store method.

While we are at it, also remove ->load_module() as it's used to load
the module before queue is freezed. Now as we moved queue-freeze under
->store(), we could load module directly from the attributes' store
method before we actually start freezing the queue. Currently, the
->load_module() is only used by "scheduler" attribute, so we now load
the relevant elevator module before we start freezing the queue in
elv_iosched_store().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250304102551.2533767-3-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>