conf/ucm: rt5651: Mute speakers on boot

conf/ucm: rt5651: Mute speakers on boot

The UCM configuration is enabling the speakers in the SectionDefaults.
This is a problem when booting with an headset already connected since
the audio output is routed at the same time both on speakers and
heaphones until the jack is disconnected and reconnected again.

Fix this disabling all the outputs in the default mixer configuration.

Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>