ACPI / LPSS: allow to use specific PM domain during ->probe()

This is an amendment to previously pushed commit 01ac170b (ACPI / LPSS:
allow to use specific PM domain during ->probe()). We can't assign anything to
the platform device on ADD_DEVICE stage since it might be changed during
unbound / bind cycle.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>