powerpc/pci: Hide pci_create_OF_bus_map() for non-chrp code

Function pci_create_OF_bus_map() is used only in chrp code.
So hide it from all other platforms.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220706104308.5390-4-pali@kernel.org