stmmac: adding DT parameter for LPI tx clock gating

This patch adds a new parameter to the stmmac DT: snps,en-tx-lpi-clockgating.
It was ported from synopsys/dwc_eth_qos.c and it is useful if lpi tx clock
gating is needed by stmmac users also.

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Tested-by: Niklas Cassel <niklas.cassel@axis.com>
Reviewed-by: Lars Persson <larper@axis.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 92ac006..fa0b4de 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -239,7 +239,8 @@
 	/* Check and enter in LPI mode */
 	if ((priv->dirty_tx == priv->cur_tx) &&
 	    (priv->tx_path_in_lpi_mode == false))
-		priv->hw->mac->set_eee_mode(priv->hw);
+		priv->hw->mac->set_eee_mode(priv->hw,
+					    priv->plat->en_tx_lpi_clockgating);
 }
 
 /**