ALSA: hda: 92hd73xx fixes

Added support for defining the number of amps and the creation
of the private_dimux dynamically for the 92hd73xx codec family.

Signed-off-by: Matthew Ranostay <mranostay@embeddedalley.com>
[Fixed a typo by tiwai]
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>