drm/msm/dp: add audio support

Add DisplayPort audio module which connects to other
modules in DisplayPort driver architecture and handles
the audio programming sequence.

CRs-Fixed: 2020938
Change-Id: I5bac1d432be0e5d517df39805dbe0bb0eb45ced2
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>