net: fsl_mdio: Correct the MII management register block address

The MII management register block offset is different between
gianfar and etsec2 compatible devices, this patch is to fix
this issue by adding driver data for different compatible
string.

Fixes: 2932c5a8 ("net: tsec: fsl_mdio: add DM MDIO support")
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>