ACPI / LPSS: add all LPSS devices to the specific power domain

Currently the LPSS devices are located in the different power domains depends
on LPSS_SAVE_CTX flag. We would like to use the specific power domain for all
LPSS devices.

The LPSS DMA controller has no knobs to control its power state. The specific
power domain implementation will handle this case. The patch does a preparation
for that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Scott Ashcroft <scott.ashcroft@talk21.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>