scsi: target: core: Add CONTROL field for trace events

trace-cmd report doesn't show events from target subsystem because
scsi_command_size() leaks through event format string:

  [target:target_sequencer_start] function scsi_command_size not defined
  [target:target_cmd_complete] function scsi_command_size not defined

Addition of scsi_command_size() to plugin_scsi.c in trace-cmd doesn't
help because an expression is used inside TP_printk(). trace-cmd event
parser doesn't understand minus sign inside [ ]:

  Error: expected ']' but read '-'

Rather than duplicating kernel code in plugin_scsi.c, provide a dedicated
field for CONTROL byte.

Link: https://lore.kernel.org/r/20200929125957.83069-1-r.bolshakov@yadro.com


Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>