ARM: dts: aspeed: bletchley: Enable mdio3 bus

Enable mdio3 bus based on EVT HW.

So far lack of c45 support in mdio-aspeed, at least can access mdio bus
by read/write register.

TODO: Add Marvell PHY 88X3310 and mdio-aspeed driver c45 support

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Patrick Williams <patrick@stwcx.xyz>
Link: https://lore.kernel.org/r/20220215163151.32252-10-potin.lai@quantatw.com


Signed-off-by: Joel Stanley <joel@jms.id.au>