mm-video: Allow devices to override QComOMXMetadata header

* Certain manufacturers add extra fields to the
  encoder_media_buffer_type struct.

Change-Id: I2485196c2ab5d798a1dcd2353c9f8cc5114987f8
hardware/qcom/media: Fix for AACEncoder CTS test failure on 7x27A

- AACEncoders CTS test fail in CTS verification.
- AAC hardware encoder is not supported due to this
  getting failed in CTS verification.
- Remove hardware AAC encoder from registry table.

Change-Id: Ie2c552308fe32c78b1cc03f454a18d015c518c34
CRs-Fixed: 457174
Merge pull request #1 from CyanogenMod/cm-11.0

kkk