Revert 'Revert "ACPICA: Permanently set _REV to the value '2'."'

Revert commit ff284f37 (Revert "ACPICA: Permanently set _REV to
the value '2'.) as the regression introduced by commit b1ef2972
reverted by it is now addressed via a blacklist entry.

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