powerpc/powernv: Move TCE manupulation code to its own file

Right now we have allocation code in pci-ioda.c and traversing code in
pci.c, let's keep them toghether. However both files are big enough
already so let's move this business to a new file.

While we at it, move the code which links IOMMU table groups to
IOMMU tables as it is not specific to any PNV PHB model.

These puts exported symbols from the new file together.

This fixes several warnings from checkpatch.pl like this:
"WARNING: Prefer 'unsigned int' to bare use of 'unsigned'".

As this is almost cut-n-paste, there should be no behavioral change.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>