ACPI: Altix: cannot register acpi bus driver before bus scan

SN code to initialize the Hub/TIO infrastructure needs to
execute before bus scanning. This was previously done with
an early call to acpi_bus_register_driver().  But now that
ACPI is using the Linux driver model, a driver cannot be registered
that early. Make changes to have the init routines invoked via
calls to acpi_get_devices().

Signed-off-by: John Keller <jpk@sgi.com>
Signed-off-by: Len Brown <len.brown@intel.com>