powerpc/85xx: MPC8572DS - Fix eTSEC is not available on core1 of AMP boot

The issue log on core1 is:
root@mpc8572ds:~# ifconfig eth0 10.192.208.244
net eth0: could not attach to PHY
SIOCSIFFLAGS: No such device

To attach PHY node mdio@24520 should not be disabled in dts of core1.
Because all PHYs are controlled through this node as follows:

mdio@24520 {
	phy0: ethernet-phy@0 {
		interrupts = <10 1 0 0>;
		reg = <0x0>;
	};
	phy1: ethernet-phy@1 {
		interrupts = <10 1 0 0>;
		reg = <0x1>;
	};
	phy2: ethernet-phy@2 {
		interrupts = <10 1 0 0>;
		reg = <0x2>;
	};
	phy3: ethernet-phy@3 {
		interrupts = <10 1 0 0>;
		reg = <0x3>;
	};

	tbi0: tbi-phy@11 {
		reg = <0x11>;
		device_type = "tbi-phy";
	};
};

Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Jia Hongtao <B38951@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/boot/dts/mpc8572ds_camp_core1.dts

@@ -67,9 +67,6 @@
 		ethernet@24000 {
 			status = "disabled";
 		};
-		mdio@24520 {
-			status = "disabled";
-		};
 		ptp_clock@24e00 {
 			status = "disabled";
 		};