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/pic32_eth.c b/drivers/net/pic32_eth.c
index 5a678d1..03eb51e 100644
--- a/drivers/net/pic32_eth.c
+++ b/drivers/net/pic32_eth.c
@@ -534,7 +534,6 @@
 {
 	struct eth_pdata *pdata = dev_get_plat(dev);
 	struct pic32eth_dev *priv = dev_get_priv(dev);
-	const char *phy_mode;
 	void __iomem *iobase;
 	fdt_addr_t addr;
 	fdt_size_t size;
@@ -550,15 +549,9 @@
 	pdata->iobase = (phys_addr_t)addr;
 
 	/* get phy mode */
-	pdata->phy_interface = -1;
-	phy_mode = fdt_getprop(gd->fdt_blob, dev_of_offset(dev), "phy-mode",
-			       NULL);
-	if (phy_mode)
-		pdata->phy_interface = phy_get_interface_by_name(phy_mode);
-	if (pdata->phy_interface == -1) {
-		debug("%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;
-	}
 
 	/* get phy addr */
 	offset = fdtdec_lookup_phandle(gd->fdt_blob, dev_of_offset(dev),