scsi: st: Separate st-unique ioctl handling from SCSI common ioctl handling

scsi: st: Separate st-unique ioctl handling from SCSI common ioctl handling

The st ioctl function currently interleaves code for handling various st
specific ioctls with parts of code needed for handling ioctls common to
all SCSI devices. Separate out st's code for the common ioctls into a
more manageable, separate function.

Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Reviewed-by: John Meneghini <jmeneghi@redhat.com>
Tested-by: John Meneghini <jmeneghi@redhat.com>
Link: https://patch.msgid.link/20251104154709.6436-1-djeffery@redhat.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>