Add llndk_stubs property

Prepare for making the relationship between an llndk_library stubs
module and the cc_library implementation module explicit by
adding an llndk_stubs property.  Each cc_library will be updated
to point to its llndk_library, and the llndk_library name will
be changed to make the .llndk suffix explicit.  Then the implicit
connection and suffix can be removed.

Bug: 170784825
Test: m checkbuild
Change-Id: I6b0482a3f286ec29b2e928551aa4317749f2b499