net: introduce helpers to get PHY interface mode from a device/ofnode

Add helpers ofnode_read_phy_mode() and dev_read_phy_mode() to parse the
"phy-mode" / "phy-connection-type" property. Add corresponding UT test.

Use them treewide.

This allows us to inline the phy_get_interface_by_name() into
ofnode_read_phy_mode(), since the former is not used anymore.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Tested-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/drivers/net/sni_netsec.c b/drivers/net/sni_netsec.c
index 4901321..693fd3a 100644
--- a/drivers/net/sni_netsec.c
+++ b/drivers/net/sni_netsec.c
@@ -1029,19 +1029,13 @@
 	struct eth_pdata *pdata = dev_get_plat(dev);
 	struct netsec_priv *priv = dev_get_priv(dev);
 	struct ofnode_phandle_args phandle_args;
-	const char *phy_mode;
 
 	pdata->iobase = dev_read_addr_index(dev, 0);
 	priv->eeprom_base = dev_read_addr_index(dev, 1) - EERPROM_MAP_OFFSET;
 
-	pdata->phy_interface = -1;
-	phy_mode = dev_read_prop(dev, "phy-mode", NULL);
-	if (phy_mode)
-		pdata->phy_interface = phy_get_interface_by_name(phy_mode);
-	if (pdata->phy_interface == -1) {
-		pr_err("%s: Invalid PHY interface '%s'\n", __func__, phy_mode);
+	pdata->phy_interface = dev_read_phy_mode(dev);
+	if (pdata->phy_interface == PHY_INTERFACE_MODE_NONE)
 		return -EINVAL;
-	}
 
 	if (!dev_read_phandle_with_args(dev, "phy-handle", NULL, 0, 0,
 					&phandle_args))