dpaa2-eth: select XGMAC_MDIO for MDIO bus support

Explicitly enable the FSL_XGMAC_MDIO Kconfig option in order to have
MDIO access to internal and external PHYs.

Fixes: 71947923 ("dpaa2-eth: add MAC/PHY support through phylink")
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/20201119145106.712761-1-ciorneiioana@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/dpaa2/Kconfig

@@ -4,6 +4,7 @@ config FSL_DPAA2_ETH
 	depends on FSL_MC_BUS && FSL_MC_DPIO
 	select PHYLINK
 	select PCS_LYNX
+	select FSL_XGMAC_MDIO
 	help
 	  This is the DPAA2 Ethernet driver supporting Freescale SoCs
 	  with DPAA2 (DataPath Acceleration Architecture v2).