PPC: Pseries: Check for PCI boundaries

We call pci_host_config_{read,write}_common() which perform PCI config
accesses. However they don't do all limit checking the way we expect
it to.

So let's introduce a small wrapper around them, making them behave the
way we would without touching generic code.

This patch is based on a patch by David Gibson which put this logic into
the generic code.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
