[ALSA] hda-codec - Rename HP model-specific quirks

Rename ALC888_HP_NETTLE and ALC888_HP_LUCKNOW models to the more generic
names ALC888_6ST_HP and ALC888_3ST_HP since HP seems to be consistent
in the wiring of their 3stack and 6stack ALC888-based systems.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>