FROMGIT: blk-mq: Introduce the BLK_MQ_F_NO_SCHED_BY_DEFAULT flag

elevator_get_default() uses the following algorithm to select an I/O
scheduler from inside add_disk():
- In case of a single hardware queue or sharing hardware queues across
  multiple request queues (BLK_MQ_F_TAG_HCTX_SHARED), use mq-deadline.
- Otherwise, use 'none'.

This is a good choice for most but not for all block drivers. Make it
possible to override the selection of mq-deadline with a new flag,
namely BLK_MQ_F_NO_SCHED_BY_DEFAULT.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Bug: 194450129
(cherry picked from commit 90b71980 git://git.kernel.dk/linux-block/

 for-5.15/block)
Change-Id: I4fb658957c193f350e74bdb5876c20a8f628fcb1
Signed-off-by: Bart Van Assche <bvanassche@google.com>