spa: group the spa headers into doxygen modules

Subdirectories buffer, control, debug, monitor, pod, support and utils, others
are still missing. Headers are grouped either per subdirectory (e.g. buffer/
gets added to group spa_buffer) or per-file (e.g. spa_json is a separate
group), whatever seemed like the most sensible approach.

spa/include/spa/param/audio/raw.h

@@ -35,6 +35,11 @@ extern "C" {
 #include <endian.h>
 #endif
 
+/**
+ * \addtogroup spa_param
+ * \{
+ */
+
 #define SPA_AUDIO_MAX_CHANNELS	64u
 
 enum spa_audio_format {
@@ -235,6 +240,10 @@ struct spa_audio_info_dsp {
 
 #define SPA_AUDIO_INFO_DSP_INIT(...)		(struct spa_audio_info_dsp) { __VA_ARGS__ }
 
+/**
+ * \}
+ */
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif