ACPI / scan: use platform bus type by default for _HID enumeration

Because of the growing demand for enumerating ACPI devices to
platform bus, change the code to enumerate ACPI device objects to
platform bus by default.  Namely, create platform devices for the
ACPI device objects that
 1. Have pnp.type.platform_id set (device objects with _HID currently).
 2. Do not have a scan handler attached.
 3. Are not SPI/I2C slave devices (that should be enumerated to the
    appropriate buses bus by their parent).

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
[rjw: Subject and changelog, rebase and code cleanup]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>