[ALSA] hda-codec - Add quirk for Asus P5LD2

Without the proper model setting, the Asus P5LD2 rear outputs remain
completely silent unlike other systems where the front speakers usually
work. This patch adds the P5LD2 to the quirk table.

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