block: Catch possible entries missing from hctx_state_name[]

Add a build-time assert that we are not missing entries from
hctx_state_name[]. For this, create a separate enum for state flags and add
a "max" entry for BLK_MQ_S_x flags.

The numbering for those enum values is as default, so don't explicitly
number.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20240719112912.3830443-10-john.g.garry@oracle.com


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