Add audio role open/close support

Rework things so that the 4A audio role is only opened while playing,
and closed when stopped.  Further work will need to be done to handle
the possibility of the output device changing on subsequent opens,
both the RTL SDR and Kingfisher case have complications around doing
so:
- The RTL SDR helper application needs to be enhanced to add an
  output setting command.  Killing it and starting it again would
  also work, but likely will add noticeable UI latency.
- On the Kingfisher, the binding currently has no control over the
  output used for the loopback, as it is being set up down in the
  soft-mixer based on HAL values.

Change-Id: I4aa83c937972ec5d91f7b78421a11148c7fe0afc
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
(cherry picked from commit f1d5902c92eafd3aad62e29298502603a9b56d81)

1 files changed, 3 insertions, 1 deletions

diff --git a/binding/radio_impl.h b/binding/radio_impl.h
index 49efe24..0216f69 100644
--- a/binding/radio_impl.h
+++ b/binding/radio_impl.h
@@ -41,7 +41,9 @@ typedef enum {
 typedef struct {
 	char *name;
 
-	int (*init)(const char *output);
+	int (*init)(void);
+
+	void (*set_output)(const char *output);
 
 	uint32_t (*get_frequency)(void);