drivers: net: stmmac: reworking the PCS code.

The 3.xx and 4.xx synopsys gmacs have a very similar
PCS embedded module and they share almost the same registers:
for example:
  AN_Control, AN_Status, AN_Advertisement, AN_Link_Partner_Ability,
  AN_Expansion, TBI_Extended_Status.

Just the RGMII/SMII Control/Status register differs.

So This patch aims to reorganize and enhance the PCS support.
It removes the existent support from the dwmac1000/dwmac4_core.c
moving basic PCS functions inside a new file called: stmmac_pcs.h.

The patch also reviews the available APIs to be better shared among
different hardware and easily enhanced to support new features.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1714,8 +1714,8 @@ static int stmmac_hw_setup(struct net_device *dev, bool init_ptp)
 		priv->hw->dma->rx_watchdog(priv->ioaddr, MAX_DMA_RIWT);
 	}
 
-	if (priv->pcs && priv->hw->mac->ctrl_ane)
-		priv->hw->mac->ctrl_ane(priv->hw, 0);
+	if (priv->pcs && priv->hw->mac->pcs_ctrl_ane)
+		priv->hw->mac->pcs_ctrl_ane(priv->hw, 1, 0, 0);
 
 	/*  set TX ring length */
 	if (priv->hw->dma->set_tx_ring_len)
@@ -2809,6 +2809,14 @@ static irqreturn_t stmmac_interrupt(int irq, void *dev_id)
 							priv->rx_tail_addr,
 							STMMAC_CHAN0);
 		}
+
+		/* PCS link status */
+		if (priv->pcs) {
+			if (priv->xstats.pcs_link)
+				netif_carrier_on(dev);
+			else
+				netif_carrier_off(dev);
+		}
 	}
 
 	/* To handle DMA interrupts */