This patch adds to support the emac phy reset.

1) phy-reset-gpios:
The phy-reset-gpios is an optional property for arc emac device tree boot.
Change the binding document to match the driver code.

2) phy-reset-duration:
Different boards may require different phy reset duration. Add property
phy-reset-duration for device tree probe, so that the boards that need
a longer reset duration can specify it in their device tree.

3) phy-reset-active-high:
We need that for a custom hardware that needs the reverse reset sequence.

Of course, this patch will fix the issue on
https://patchwork.kernel.org/patch/8186801/.

In some cases, the emac couldn't work if you don't have reset the phy.
Let's add it to happy work.

Signed-off-by: Caesar Wang <redacted>
---

  drivers/net/ethernet/arc/emac_main.c | 41 ++++++++++++++++++++++++++++++++++++
  1 file changed, 41 insertions(+)

diff --git a/drivers/net/ethernet/arc/emac_main.c b/drivers/net/ethernet/arc/emac_main.c
index 6446af1..42384f6a 100644
--- a/drivers/net/ethernet/arc/emac_main.c
+++ b/drivers/net/ethernet/arc/emac_main.c

@@ -764,6 +764,45 @@ static const struct net_device_ops arc_emac_netdev_ops = {
  #endif
  };

+#ifdef CONFIG_OF
+static void emac_reset_phy(struct net_device *pdev)
+{
+	int err, phy_reset;
+	bool active_high = false;
+	int msec = 10;
+	struct device *dev = pdev->dev.parent;
+	struct device_node *np = dev->of_node;
+
+	if (!np)
+		return;
+
+	of_property_read_u32(np, "phy-reset-duration", &msec);
+	/* A sane reset duration should not be longer than 1s */
+	if (msec > 1000)
+		msec = 1;
+
+	phy_reset = of_get_named_gpio(np, "phy-reset-gpios", 0);
+	if (!gpio_is_valid(phy_reset))
+		return;
+
+	active_high = of_property_read_bool(np, "phy-reset-active-high");
+
+	err = devm_gpio_request_one(dev, phy_reset, active_high ?
+				    GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW,
+				    "phy-reset");
+	if (err) {
+		dev_err(dev, "failed to get phy-reset-gpios: %d\n", err);
+		return;
+	}
+	msleep(msec);
+	gpio_set_value_cansleep(phy_reset, !active_high);
+}