Convert libaudioflinger to Android.bp

This makes the libaudioflinger build deterministic between
devices.

A few notes:
- the include-path-for include is obsolete, so it was removed
- the AUDIOSERVER_MULTILIB use was removed, as I believe it's
  unused

Bug: 121208203
Test: make
Change-Id: I08eb0d7f53f1fbcef3e14faa3ea75b5326383ef8