Sync ACPICA with Intel's version 20151218.

Sync ACPICA with Intel's version 20151218.

* Execute "module-level code" as ACPI tables are loaded into the
  namespace during initialization and install the default operation
  region handlers for the SystemMemory, SystemIO and PCI_Config
  address spaces before any ACPI tables are loaded (in order to
  enable module-level code to access these address spaces). Also,
  several changes to the internal _REG support and to utilities
  in conjunction with these changes.

* Various other fixes and features.

For a more detailed list, please see sys/contrib/dev/acpica/changes.txt.