mm-core: Remove double declaration of OMX.qcom.audio.decoder.aac

Change-Id: I0d64cde98ab92c48fe9e70d26724c334f22a79f6
mm-video: Allow devices to override QComOMXMetadata header

* Certain manufacturers add extra fields to the
  encoder_media_buffer_type struct.

Change-Id: I2485196c2ab5d798a1dcd2353c9f8cc5114987f8