ACPI / scan: Consolidate extraction of power resources lists

The lists of ACPI power resources are currently extracted in two
different ways, one for wakeup power resources and one for power
resources that device power states depend on.  There is no reason
why it should be done differently in those two cases, so introduce
a common routine for extracting power resources lists from data
returned by AML, acpi_extract_power_resources(), and make the
namespace scanning code use it for both wakeup and device power
states power resources.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>