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/support/log-impl.h

@@ -34,6 +34,11 @@ extern "C" {
 #include <spa/utils/type.h>
 #include <spa/support/log.h>
 
+/**
+ * \addtogroup spa_log
+ * \{
+ */
+
 static inline SPA_PRINTF_FUNC(6, 0) void spa_log_impl_logv(void *object,
 				     enum spa_log_level level,
 				     const char *file,
@@ -87,6 +92,10 @@ struct {					\
 #define SPA_LOG_IMPL(name)			\
         SPA_LOG_IMPL_DEFINE(name) = SPA_LOG_IMPL_INIT(name)
 
+/**
+ * \}
+ */
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif