powerpc/85xx: Enable support for ports 3 and 4 on 8548 CDS

I believe support was disabled due to issues with earlier versions of
the board/processor.  At worst, adding the ports back into the device
tree should result in enabling ports that don't work on older systems,
so the default should be to enable them.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>