msm7x30: Add local copy of audio HAL and build it

* CM's audio-caf is outdated and our msm7x30 patches won't get merged anytime soon
* We need to set the TARGET_QCOM_AUDIO_VARIANT flag to caf in order to use all
  qcom features but that conflicts with the code in hardware/qcom/audio-caf
* Add a local copy of the audio HAL, renamed from msm7x30 to semc & build it

Change-Id: I8cd98bbb74edeed4282ef20cc44b769da167374b