Implement spapr pci for little endian systems.

Port the spapr_pci implementation for ppc64le.
Based on suggestions by Alexey Kardashevskiy <aik@ozlabs.ru>
We should have always used phys_hi and 64 bit addr and size.

Cc: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Will Deacon <will.deacon@arm.com>