Add libaudiofoundation.

Some classes, e.g. AudioGain, in libaudiofoundation, which are used by
libaudiopolicycomponent, will require libaudiofoundation as a shared
library to avoid link error when building.

Bug: 135621476
Test: make
Change-Id: I8732bdab37d8afd866fe03a74db3dc564fea1ad2
Merged-In: I8732bdab37d8afd866fe03a74db3dc564fea1ad2