powerpc/powernv: Shift VF resource with an offset

On PowerNV platform, resource position in M64 BAR implies the PE# the
resource belongs to. In some cases, adjustment of a resource is necessary
to locate it to a correct position in M64 BAR .

This patch adds pnv_pci_vf_resource_shift() to shift the 'real' PF IOV BAR
address according to an offset.

Note:

    After doing so, there would be a "hole" in the /proc/iomem when offset
    is a positive value. It looks like the device return some mmio back to
    the system, which actually no one could use it.

[bhelgaas: rework loops, rework overlap check, index resource[]
conventionally, remove pci_regs.h include, squashed with next patch]
Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>