Add the item of i915_component.h in DocBook and add the DOC for
i915_component.h. Explain the struct i915_audio_component_ops and
struct i915_audio_component_audio_ops usage.
Signed-off-by: NLibin Yang <libin.yang@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>