ARM: dts: aspeed: elbert: Enable mac3 controller

Enable mac3 controller in Elbert dts: Elbert MAC3 is connected to the
BCM53134P onboard switch's IMP_RGMII port directly (fixed link, no PHY
between BMC MAC and BCM53134P).

Note: BMC's mdio0 controller is connected to BCM53134P's MDIO interface,
and the MDIO channel will be enabled later, when BCM53134 is added to
"bcm53xx" DSA driver.
Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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

@@ -183,3 +183,21 @@ imux31: i2c@7 {
 &i2c11 {
 	status = "okay";
 };
+
+/*
+ * BMC's "mac3" controller is connected to BCM53134P's IMP_RGMII port
+ * directly (fixed link, no PHY in between).
+ * Note: BMC's "mdio0" controller is connected to BCM53134P's MDIO
+ * interface, and the MDIO channel will be enabled in dts later, when
+ * BCM53134 is added to "bcm53xx" DSA driver.
+ */
+&mac3 {
+	status = "okay";
+	phy-mode = "rgmii";
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_rgmii4_default>;
+	fixed-link {
+		speed = <1000>;
+		full-duplex;
+	};
+};