apex: add llndk libs as requireNativeLibs

"use_vendor: true" APEX modules may bundle vendor variants of cc
modules, which can depend on llndk stubs.

In that case, those llndk libraries should be also counted as required
libraries. (stored in 'requireNativeLibs' key in apex_manifest.json)

Bug: 138695532
Test: m nothing (runs soong tests)
Change-Id: If7ad4dec0e723c8d0c73ca60453b555063e14694