null_blk: Move driver into its own directory

stable inclusion
from stable-v5.10.176
commit d14d2574a54c2ee7ae6c44a5507973972ecce7f5
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8CHVQ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d14d2574a54c2ee7ae6c44a5507973972ecce7f5



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[ Upstream commit eebf34a8 ]

Move null_blk driver code into the new sub-directory
drivers/block/null_blk.

Suggested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: 63f88659 ("block: null_blk: Fix handling of fake timeout request")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>