general: recoded snd_dlobj_ functions

- changed logic to get/put blocks
- added mutex locking of the symbol list
- added reference counting (do not free used dl handles)

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/pcm/pcm_local.h

@@ -174,7 +174,7 @@ typedef struct {
 } snd_pcm_fast_ops_t;
 
 struct _snd_pcm {
-	void *dl_handle;
+	void *open_func;
 	char *name;
 	snd_pcm_type_t type;
 	snd_pcm_stream_t stream;