ACPI: introduce helper interfaces for _DSM method

There are several drivers making use of ACPI _DSM method to detect
and invoke device specific methods. Currently every driver has
implemented its private version to support ACPI _DSM method.
So this patch introduces three helper functions to support ACPI _DSM
method, which will be used to replace open-coded versions.

It helps to simplify code and improve code readability.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>