PCI: add generic pci_enable_resources()

Each architecture has its own pcibios_enable_resources() implementation.
These differ in many minor ways that have nothing to do with actual
architectural differences.  Follow-on patches will make most arches
use this generic version instead.

This version is based on powerpc, which seemed most up-to-date.  The only
functional difference from the x86 version is that this uses "!r->parent"
to check for resource collisions instead of "!r->start && r->end".

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>