ALSA: x86: hdmi: continue playback even when display resolution changes

ALSA: x86: hdmi: continue playback even when display resolution changes

When the display resolution changes, the drm disables the
display pipes due to which audio rendering stops. At this
time, we need to ensure the existing audio pointers and
buffers are cleared out so that the playback can restarted
once the display pipe is enabled with a different N/CTS values

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Jerome Anand <jerome.anand@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>