powerpc/44x: Enable 64bit (>= 4GB) memory size in Katmai dts

Additionally to increasing #size-cells to in the root node, we also
need to explicitly define the ranges property in the plb node, because
of the different #size-cells between child and parent.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>