block/cgroup: Improve lock context annotations

block/cgroup: Improve lock context annotations

Add lock context annotations where these are missing. Move the
blkg_conf_prep() annotation into block/blk-cgroup.h to make it visible
to all blkg_conf_prep() callers.

Reviewed-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://patch.msgid.link/58ddd6e2b960bdfa03d0007984386bc0ba351391.1780682325.git.bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>