ALSA: hda - Add suffix argument to snd_hda_add_vmaster()

In most cases, the slave strings for vmaster are identical between
volumes and switches except for "xxx Volume" and "xxx Switch" suffix.
Now snd_hda_add_vmaster() takes the optional suffix argument so that
each string can be composed with the given suffix, and we can share the
slave name strings in both volume and switch calls nicely.

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