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

arch/arm/boot/dts/aspeed-bmc-facebook-bletchley.dts

@@ -840,3 +840,8 @@
 		&pinctrl_adc12_default &pinctrl_adc13_default
 		&pinctrl_adc14_default &pinctrl_adc15_default>;
 };
+
+&mdio3 {
+	status = "okay";
+	/* TODO: Add Marvell 88X3310 */
+};