ALSA: hda - Rewrite the mute-LED hook with vmaster hook in patch_sigmatel.c

The mute-LED is controlled in patch_sigmatel.c by (ab-)using the
powersave hook.  This can be now rewritten with the vmaster hook
instead, which is much simpler and can work even without
CONFIG_SND_HDA_POWER_SAVE kconfig.

A drawback is that the mute-LED corresponds _only_ to the Master mixer
switch instead of checking the whole DACs.  But usually this shouldn't
be a big problem as PA enables the mixer elements accordingly.

Also, this patch changes the code to create vmaster always even on
STAC9200 and STAC925x.  The former "Master" on these chips are renamed
as "PCM" now.

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