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/control/control.h

@@ -32,10 +32,15 @@ extern "C" {
 #include <spa/utils/defs.h>
 #include <spa/pod/pod.h>
 
-/** Controls
+/** \defgroup spa_control SPA Controls
  *
  */
 
+/**
+ * \addtogroup spa_control
+ * \{
+ */
+
 /** Different Control types */
 enum spa_control_type {
 	SPA_CONTROL_Invalid,
@@ -46,6 +51,10 @@ enum spa_control_type {
 	_SPA_CONTROL_LAST,		/**< not part of ABI */
 };
 
+/**
+ * \}
+ */
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif

spa/include/spa/control/type-info.h

@@ -29,6 +29,11 @@
 extern "C" {
 #endif
 
+/**
+ * \addtogroup spa_control
+ * \{
+ */
+
 #include <spa/utils/defs.h>
 #include <spa/utils/type-info.h>
 #include <spa/control/control.h>
@@ -45,6 +50,10 @@ static const struct spa_type_info spa_type_control[] = {
 	{ 0, 0, NULL, NULL },
 };
 
+/**
+ * \}
+ */
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif