ASoC: cs42l51: add dac mux widget in codec routes

Add "DAC mux" DAPM widget in CS42l51 audio codec routes,
to support DAC mux control and to remove error trace
"DAC Mux has no paths" at widget creation.
Note: ADC path of DAC mux is not routed in this patch.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Link: https://lore.kernel.org/r/20191203141627.29471-1-olivier.moysan@st.com


Signed-off-by: Mark Brown <broonie@kernel.org>