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.

In this change, following libs were made available to all apexes because
their usage is quite common and there is no reason to restrict them
to some APEXes.

* libbase_headers
* libcutils, libcutils_headers
* libutils_headers, libsystem_headers
* liblog_headers
* libbacktrace, libbacktrace_headers
* libcrypto_utils

Bug: 150999716
Test: m
Change-Id: If3d3652e6604ed4f6d7694fe7ac61ae496621026