It's easier to violate abstractions and introduce bugs when snoc.h is
including pci.h. Let's not do that.

I'm not extremely familiar with this driver yet, but several of the
shared PCI/SNOC bits seem to be related to the Copy Engine, so move them
to ce.h.
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>