x86/PCI: Factor out pcibios_allocate_dev_resources()

Factor pcibios_allocate_dev_resources() out of
pcibios_allocate_resources().  Currently we only allocate these
resources at boot-time with a for_each_pci_dev() loop.  Eventually
we'll use pcibios_allocate_dev_resources() for hot-added devices, too.

[bhelgaas: changelog]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>