greybus: audio: Use AIF widget to enable path between module & APB

Currently, SPK Amp switch is used to identify when to enable data path
between module and APB. With headset, other switch controls added, it is
not possible to use this switch to control data path. Instead path
should be established based on AIF widget.

Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>