gianfar: Add Scatter Gather support

Scatter Gather support in gianfar driver to handle fragmented frames on
the transmit side.

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Dai Haruki <dai.haruki@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/gianfar.h b/drivers/net/gianfar.h
index 9c8974d..7ef3cc5 100644
--- a/drivers/net/gianfar.h
+++ b/drivers/net/gianfar.h
@@ -728,6 +728,7 @@
 	struct txbd8 *dirty_tx;		/* First buffer in line
 					   to be transmitted */
 	unsigned int tx_ring_size;
+	unsigned int num_txbdfree;	/* number of TxBDs free */
 
 	/* RX Locked fields */
 	spinlock_t rxlock;