caif-hsi: Add RX flip buffer

Implement RX flip buffer in the cfhsi_rx_done function,
piggy-backed frames is also supported.
This gives a significant performance gain for CAIF over HSI.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/caif/caif_hsi.h b/include/net/caif/caif_hsi.h
index 8d55251..6db8ecf 100644
--- a/include/net/caif/caif_hsi.h
+++ b/include/net/caif/caif_hsi.h
@@ -138,6 +138,7 @@
 	u8 *rx_ptr;
 	u8 *tx_buf;
 	u8 *rx_buf;
+	u8 *rx_flip_buf;
 	spinlock_t lock;
 	int flow_off_sent;
 	u32 q_low_mark;