fs_enet: Be an of_platform device when CONFIG_PPC_CPM_NEW_BINDING is set.

The existing OF glue code was crufty and broken.  Rather than fix it, it
will be removed, and the ethernet driver now talks to the device tree
directly.

The old, non-CONFIG_PPC_CPM_NEW_BINDING code can go away once CPM
platforms are dropped from arch/ppc (which will hopefully be soon), and
existing arch/powerpc boards that I wasn't able to test on for this
patchset get converted (which should be even sooner).

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>