ACPI: call acpi_scan_init() explicitly rather than as initcall

This patch makes acpi_init() call acpi_scan_init() directly.

Previously, both acpi_init() and acpi_scan_init() were subsys_initcalls,
and acpi_init() was called first based on the link order from the
makefile (bus.o before scan.o).

acpi_scan_init() registers the ACPI bus type, creates the root device,
and enumerates fixed-feature and namespace devices.  All of this must
be done after acpi_init(), and it's better to call acpi_scan_init()
explicitly rather than rely on the link ordering.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>