drivers: net: add NXP ENETC MDIO driver

Adds a driver for the MDIO interface currently integrated in LS1028A SoC.
This MDIO interface is shared by multiple ethernet interfaces and is
presented as a stand-alone PCI function on the SoC ECAM.
Ethernet has a functional dependency on MDIO, for simplicity there is a
single config option for both.

Signed-off-by: Alex Marginean <alexm.osslist@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 802eadf..4d85fb1 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -590,7 +590,7 @@
 
 config FSL_ENETC
 	bool "NXP ENETC Ethernet controller"
-	depends on DM_PCI && DM_ETH
+	depends on DM_PCI && DM_ETH && DM_MDIO
 	help
 	  This driver supports the NXP ENETC Ethernet controller found on some
 	  of the NXP SoCs.