Mark CTL frontend's CAM driver as CAM_PERIPH_DRV_EARLY.

Target mode operation does not depend on the initiator mode scan process.
This change allows the target driver to attach earlier and receive some
async events (like AC_CONTRACT) that could be lost otherwise.

MFC after:	1 week

sys/cam/ctl/scsi_ctl.c

@@ -224,7 +224,8 @@ static void 		ctlfe_dump(void);
 static struct periph_driver ctlfe_driver =
 {
 	ctlfeperiphinit, "ctl",
-	TAILQ_HEAD_INITIALIZER(ctlfe_driver.units), /*generation*/ 0
+	TAILQ_HEAD_INITIALIZER(ctlfe_driver.units), /*generation*/ 0,
+	CAM_PERIPH_DRV_EARLY
 };
 
 static struct ctl_frontend ctlfe_frontend =