audio: Add a separate HAL for HDMI audio

Creating an audio HAL for HDMI because:

  * The HDMI card is already a separate card from
    the OMAP ABE audio.

  * The needs of HDMI are getting more specialized
    (e.g. things like multichannel audio, bitstream
    audio, etc.)

  * Things in the OMAP ABE HAL are getting a bit
    cramped and complex, and it would be better to
    reduce the complexity rather than add to it.

This version is provides the same functionality as audio_hw.c

Change-Id: Ifcf1cca4f7f49bcabc14c20105a9ddc40f2e33e3
Signed-off-by: Gabriel M. Beddingfield <gabrbedd@ti.com>