libqos: Isolate knowledge of spapr memory map to qpci_init_spapr()

libqos: Isolate knowledge of spapr memory map to qpci_init_spapr()

The libqos code for accessing PCI on the spapr machine type uses IOBASE()
and MMIOBASE() macros to determine the address in the CPU memory map of
the windows to PCI address space.

This is a detail of the implementation of PCI in the machine type, it's not
specified by the PAPR standard.  Real guests would get the addresses of the
PCI windows from the device tree.

Finding the device tree in libqos would be awkward, but we can at least
localize this knowledge of the implementation to the init function, saving
it in the QPCIBusSPAPR structure for use by the accessors.

That leaves only one place to fix if we alter the location of the PCI
windows, as we're planning to do.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>