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 <[e-mail]>
Signed-off-by: Jia Hongtao <[e-mail]>
Signed-off-by: Kumar Gala <[e-mail]>

arch/powerpc/boot/dts/mpc8572ds_camp_core1.dts

···
 		ethernet@24000 {
 			status = "disabled";
 		};
-		mdio@24520 {
-			status = "disabled";
-		};
 		ptp_clock@24e00 {
 			status = "disabled";
 		};