Add support when LOCAL_PRIVATE_PLATFORM_APIS is true.

LOCAL_PRIVATE_PLATFORM_APIS := ture means that the apps or packages can
use the private API. So, if LOCAL_PRIVATE_PLATFORM_APIS := true, they
are linked to ".impl" instead of ".stub".

Bug: 77577799
Test: build
Change-Id: I782e52078bb8c4139c3a24862cb381f6a84e53fe