[POWERPC] cpm_uart: 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 has been removed, and the serial driver now talks to the device tree
directly.

The 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: Kumar Gala <galak@kernel.crashing.org>