ALSA: hda - Headphone mic support for an Asus/Conexant device

This Conexant codec has a single jack that can be used as either
headphone or mic (but not headset). The existing hp_mic functionality
does not apply here, because the mic and the HP are on separate pins.

Hence make a lighter version of what has been earlier done for Realtek
codecs.

BugLink: https://bugs.launchpad.net/bugs/1198030
Tested-by: Franz Hsieh <franz.hsieh@canonical.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>