net: mdio-uclass: add wrappers for read/write/reset operations

Add wrappers dm_mdio_read(), dm_mdio_write() and dm_mdio_reset() for
DM MDIO's .read(), .write() and .reset() operations.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>