scsi: documentation: add scsi_common.c to SCSI driver-api

Add exported functions from scsi_common.c to the SCSI driver API
documentation.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/driver-api/scsi.rst

@@ -224,6 +224,14 @@ mid to lowlevel SCSI driver interface
 .. kernel-doc:: drivers/scsi/hosts.c
    :export:
 
+drivers/scsi/scsi_common.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+general support functions
+
+.. kernel-doc:: drivers/scsi/scsi_common.c
+   :export:
+
 Transport classes
 -----------------