stmmac: add HW DMA feature register (v3)

New GMAC chips have an extra register to indicate
the presence of the optional features/functions of
the DMA core.

This patch adds this support and all the HW cap
are exported via debugfs.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index ef03796..c3a2da7 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -78,6 +78,7 @@
 #endif
 	struct plat_stmmacenet_data *plat;
 	struct stmmac_counters mmc;
+	struct dma_features dma_cap;
 };
 
 extern int stmmac_mdio_unregister(struct net_device *ndev);