greybus: audio: add runtime pm to enumerated control and DAPM widget

There's an issue that the userspace is not able to control both the
enumerated control and DAPM widget when audio bundle is in the SUSPEND
state. This patch fixes the issue by adding pm_runtime_get/put() calls
for the both controls.

Testing Done:
 - Use tinymix to get and put both enumerated control and DAPM widget as
   the followings, and observe audio bundle is able to wake up from
   suspend.

$ tinymix "GB 3 PB source" 1
$ tinymix "GB 3 PB source"
GB 3 PB source:	AIF1	>AIF2

$ tinymix "GB 3 AIF1_RX MUX" 2
$ tinymix "GB 3 AIF1_RX MUX"
GB 3 AIF1_RX MUX:	Stereo	Left	>Right

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