powerpc/83xx: mpc836x - fix failed phy detection for ucc ethernet on MDS

The mpc836x_mds platform has been broken since the commit
6fe32649

  "netdev/phy: Use mdiobus_read() so that proper locks are taken"

which caused the fsl_pq_mdio TBI autoprobe to oops.  The oops
was "fixed" in commit 28d8ea2d

  "fsl_pq_mdio: Clean up tbi address configuration"

by simply removing the the autoscan code, and making tbi nodes
mandatory.  Some of the newer reference platforms were updated
to have tbi nodes in 22066949

  "powerpc: Add TBI PHY node to first MDIO bus"

but the older mpc836x didn't get one and hence was just failing
with -EBUSY as follows:

 fsl-pq_mdio: probe of e0102120.mdio failed with error -16
   ...
 net eth0: Could not attach to PHY
 eth0: Cannot initialize PHY, aborting.

Add a TBI node and use the 1st free address for it.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/boot/dts/mpc836x_mds.dts

@@ -405,6 +405,10 @@ phy1: ethernet-phy@01 {
 				reg = <0x1>;
 				device_type = "ethernet-phy";
 			};
+			tbi-phy@2 {
+				device_type = "tbi-phy";
+				reg = <0x2>;
+			};
 		};
 
 		qeic: interrupt-controller@80 {