ALSA: hda/realtek - Assign Master mixer when possible

There are a few more cases where we can assign "Master" mixer element
safely, e.g. when a single DAC is used in the whole output paths.

Also, when vmaster hook is present, avoid "Master" but assign "PCM"
instead.  Otherwise vmaster hook won't work properly.

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