Revert "PM: domains: Fix up terminology with parent/child"

This reverts commit 35a2681e which is
commit 8d87ae48ced2dffd5e7247d19eb4c88be6f1c6f1 upstream.

It is not needed in Android systems, and it breaks the ABI for no real
reason, so revert it.

Bug: 161946584
Change-Id: I50c760760dad7e4fbbec88814d66b36445928771
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>