ALSA: hda - Sync EAPD with vmaster on AD1984A Thinkpads

As EAPD on NID 0x12 (speaker pin) is used as the master amp on
Thinkpads with AD1984A codec, we can hook this to vmaster for saving a
bit more power at master mute state.

Signed-off-by: Takashi Iwai <tiwai@suse.de>