ASoC: tas5086: add DAPM mux controls

The TAS5086 has two muxes, one for connecting I2S inputs to internal
channels, and another one for selecting which internal channel should
be routed to which PWM output pin.

This patch adds DAPM widgets and routes for this driver.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>