Set apex_available property

The marked library(ies) were available to the APEXes via the
hand-written whitelist in build/soong/apex/apex.go. Trying to remove the
whitelist by adding apex_available property to the Android.bp of the
libraries.

Exempt-From-Owner-Approval: approved by enh

Bug: 150999716
Test: m
Merged-In: I022ce8459039c11f62d7f7f4e6e1a822489da953
Change-Id: I5a6070ad03768575c9b5980b3e03ddc3d222e119