Track the offsets of the bus -> CPU mapping for I/O and memory.  This is
cosmetic for current Tegra chips because the offset is always 0.  But to
properly support legacy use-cases, like VGA, this would be needed so that
PCI bus addresses can be relocated.

While at it, also request the I/O resource both in physical memory and I/O
space to make /proc/iomem consistent, as well as add the I/O region to the
list of host bridge resources.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>