ALSA: hda-intel: reorder HDMI audio enabling sequence

Reorder HDMI audio enabling sequence so that
	1) the sink knows about the coming audio stream
	2) unmute
	3) start transferring audio samples

The theory is that in the path A=>B=>C, we first make C ready, and then
enable B, and lastly allow A to send audio samples.

Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>