libhardware: add libaudio_system_headers

hardware/audio.h uses libaudio_system_headers

Test: works with BOARD_VNDK_VERSION := current
Bug: 33241851
(cherry picked from commit d24879050a28098a8a20a64d9f25e2574df180d2)
Merged-In: I6042c9903b2bc580ec519b713f0f19d94e1daa2d
Change-Id: I6042c9903b2bc580ec519b713f0f19d94e1daa2d
1 file changed