imx: ventana: make RS232 enable board specific

Not all Ventana boards have an RS232 transceiver, make it board specific.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
diff --git a/board/gateworks/gw_ventana/common.h b/board/gateworks/gw_ventana/common.h
index d037767..389d3aa 100644
--- a/board/gateworks/gw_ventana/common.h
+++ b/board/gateworks/gw_ventana/common.h
@@ -78,6 +78,8 @@
 	int usb_sel;
 	int wdis;
 	int msata_en;
+	int rs232_en;
+	/* various features */
 	bool usd_vsel;
 };