Reconfigure and restart audio when display is enabled, if audio
playback was active before. This is needed in a situation when an
audio+video stream application opens the audio stream before the
video. When video stream is opened the display mode may change and
that aborts audio playback, because the display is momentarily
turned off.

The audio configuration is stored when it is successfully applied and
a boolean is set when the audio playback is started and unset when
stopped. This data is used to reconfigure the audio when display is
re-enabled. The audio playback is aborted if the reconfiguration fails.

A new spin lock is introduced in order to protect state variables
related to audio playback status. This is needed for the transition
from display enabled state (when audio start/stop commands can be
written to HW) to display disabled state (when audio start/stop
commands update only the hdmi.audio_playing variable) to always
serialize correctly with the start/stop audio commands. The already
existing mutex can not be used, because the audio start and stop
commands are executed in atomic context.

For example: when display is turned back on we take the spinlock and
we can be sure that the audio start/stop status will not change while
we update the HW according to hdmi.audio_playing state and set
hdmi.display_enabled to true. After releasing the lock
hdmi.display_enabled is true and all audio_start and audio_stop
commands write their stuff directly to HW.
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>