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/format-utils.h

@@ -30,6 +30,11 @@ extern "C" {
 #endif
 
 
+/**
+ * \addtogroup spa_param
+ * \{
+ */
+
 #include <spa/pod/parser.h>
 #include <spa/param/format.h>
 
@@ -42,6 +47,10 @@ spa_format_parse(const struct spa_pod *format, uint32_t *media_type, uint32_t *m
 		SPA_FORMAT_mediaSubtype, SPA_POD_Id(media_subtype));
 }
 
+/**
+ * \}
+ */
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif