OMAPDSS: HDMI: Decouple wrapper enable/disable and audio start/stop

Decouple the enable/disable operation of the HDMI audio wrapper from
audio start/stop. Otherwise, an audio FIFO underflow may occur. The
audio wrapper enablement must be done after configuration and
before audio playback is started.

Signed-off-by: Axel Castaneda Gonzalez <x0055901@ti.com>
Signed-off-by: Ricardo Neri <ricardo.neri@ti.com>