Altix: Add initial ACPI IO support

First phase in introducing ACPI support to SN.
In this phase, when running with an ACPI capable PROM,
the DSDT will define the root busses and all SN nodes
(SGIHUB, SGITIO). An ACPI bus driver will be registered
for the node devices, with the acpi_pci_root_driver being
used for the root busses. An ACPI vendor descriptor is
now used to pass platform specific information for both
nodes and busses, eliminating the need for the current
SAL calls. Also, with ACPI support, SN fixup code is no longer
needed to initiate the PCI bus scans, as the acpi_pci_root_driver
does that.

However, to maintain backward compatibility with non-ACPI capable
PROMs, none of the current 'fixup' code can been deleted, though
much restructuring has been done. For example, the bulk of the code
in io_common.c is relocated code that is now common regardless
of what PROM is running, while io_acpi_init.c and io_init.c contain
routines specific to an ACPI or non ACPI capable PROM respectively.

A new pci bus fixup platform vector has been created to provide
a hook for invoking platform specific bus fixup from pcibios_fixup_bus().

The size of io_space[] has been increased to support systems with
large IO configurations.

Signed-off-by: John Keller <jpk@sgi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>