net: mvneta: Use DM MDIO API for connecting PHY

Use the modern DM MDIO API for connecting PHY in the mvneta driver.

This requires enabling MVMDIO driver in several config files.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/db-88f6820-gp_defconfig b/configs/db-88f6820-gp_defconfig
index 2dcbc2f..f56d1fb 100644
--- a/configs/db-88f6820-gp_defconfig
+++ b/configs/db-88f6820-gp_defconfig
@@ -62,6 +62,7 @@
 CONFIG_PHY_GIGE=y
 CONFIG_MVNETA=y
 CONFIG_MII=y
+CONFIG_MVMDIO=y
 CONFIG_PCI=y
 CONFIG_PCI_MVEBU=y
 CONFIG_SCSI=y