net: fec_mxc: Add board_interface_eth_init() for i.MX8M Mini/Nano/Plus

Implement common board_interface_eth_init() and call it from the FEC
driver to configure IOMUXC GPR[1] register according to the PHY mode
obtained from DT. This supports all three interface modes supported by
the i.MX8M Mini/Nano/Plus FEC and supersedes the current board-side
configuration of the same IOMUX GPR[1] duplicated in the board files.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c
index 7a85771..ac93767 100644
--- a/drivers/net/fec_mxc.c
+++ b/drivers/net/fec_mxc.c
@@ -1232,6 +1232,10 @@
 	uint32_t start;
 	int ret;
 
+	ret = board_interface_eth_init(dev, pdata->phy_interface);
+	if (ret)
+		return ret;
+
 	if (IS_ENABLED(CONFIG_IMX_MODULE_FUSE)) {
 		if (enet_fused((ulong)priv->eth)) {
 			printf("SoC fuse indicates Ethernet@0x%lx is unavailable.\n", (ulong)priv->eth);