scsi_debug: support scsi-mq, queues and locks

 - add host_lock option whose default value is 0 which removes the
   host_lock around all queued commands
 - accept delay=-1 (_hi_) or -2 which use a tasklet to invoke
   the scsi_done callback into the mid-layer. The default
   is still delay=1 which uses a timer to delay 1 jiffy
 - wire .change_queue_depth and .change_queue_type
   functions to better simulate queueing in a modern LLD
 - add SCSI_DEBUG_OPT_Q_NOISE (0x200) mask to only produce
   debug output associated with queue full, plus from
   .change_queue_depth and .change_queue_type functions
 - add SCSI_DEBUG_OPT_ALL_TSF (0x400) mask which reports
   all queued_arr fulls at TASK_SET_FULL, otherwise
   SCSI_MLQUEUE_HOST_BUSY is returned
 - add SCSI_DEBUG_OPT_RARE_TSF (0x800) mask which works
   together with the every_nth option (> 0) to count
   occurrences of num_in_q==queue_depth. When every_nth
   is reached the victim (a command) yields TASK SET FULL
 - clean up many debug messages.
 - add ndelay=<nanosecs> option that uses high resolution
   timers; active if > 0 and then overrides delay= option
 - expand Unit Attention handling: POR, BUS_RESET and
   MODE PARAMETERS CHANGED
 - support .eh_target_reset_handler and drop .bios_param
 - add OPT_N_WCE mask so caching page yields WCE=0
 - add OPT_RESET_NOISE mask to log aborts and resets
 - add OPT_NO_CDB_NOISE mask to not log each cdb
 - MODE SELECT support for changing caching page's WCE
 - name common ioctls in log
 - when fake_rw=1, do not vmalloc fake store; make
   UNMAP and WRITE SAME obey fake_rw
 - more logging and code improvements including better
   sense buffer handling

With fio and four (pseudo) devices I have observed 1.2 M IOPS
on my equipment. Rob Elliott who has done much testing and made
numerous suggestions, has better IOPS results than mine.
Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Robert Elliott <elliott@hp.com>
Tested-by: Robert Elliott <elliott@hp.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>