net: fec_mxc: Add ref clock setup support for i.MX8M Mini/Nano/Plus

The FEC ref clock frequency on i.MX8M Mini/Nano/Plus was so far configured
via ad-hoc board code. Replace that with DM clock clk_set_rate() instead.
This way, the driver claims all its required clock and sets the ref clock
rate, without any need of architecture specific register fiddling.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c
index 1a6c18a..7a85771 100644
--- a/drivers/net/fec_mxc.c
+++ b/drivers/net/fec_mxc.c
@@ -1196,6 +1196,33 @@
 }
 #endif
 
+static int fecmxc_set_ref_clk(struct clk *clk_ref, phy_interface_t interface)
+{
+	unsigned int freq;
+	int ret;
+
+	if (!CONFIG_IS_ENABLED(CLK_CCF))
+		return 0;
+
+	if (interface == PHY_INTERFACE_MODE_MII)
+		freq = 25000000;
+	else if (interface == PHY_INTERFACE_MODE_RMII)
+		freq = 50000000;
+	else if (interface == PHY_INTERFACE_MODE_RGMII ||
+		 interface == PHY_INTERFACE_MODE_RGMII_ID ||
+		 interface == PHY_INTERFACE_MODE_RGMII_RXID ||
+		 interface == PHY_INTERFACE_MODE_RGMII_TXID)
+		freq = 125000000;
+	else
+		return -EINVAL;
+
+	ret = clk_set_rate(clk_ref, freq);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
 static int fecmxc_probe(struct udevice *dev)
 {
 	bool dm_mii_bus = true;
@@ -1253,6 +1280,11 @@
 
 		ret = clk_get_by_name(dev, "enet_clk_ref", &priv->clk_ref);
 		if (!ret) {
+			ret = fecmxc_set_ref_clk(&priv->clk_ref,
+						 pdata->phy_interface);
+			if (ret)
+				return ret;
+
 			ret = clk_enable(&priv->clk_ref);
 			if (ret)
 				return ret;