parameters: new parameter server backend

- parameter backend is now running in a wq and accessible over pub/sub
 - parameters library can call into backend directly (with locking), but operations will gradually start moving to pub/sub
 - majority of parameters migrated as is, only small changes to parameter autosave and parameter notification that are now performed from the WQ thread

platforms/nuttx/src/px4/common/px4_init.cpp

@@ -127,8 +127,6 @@ int px4_platform_init()
 	hrt_ioctl_init();
 #endif
 
-	param_init();
-
 	/* configure CPU load estimation */
 #ifdef CONFIG_SCHED_INSTRUMENTATION
 	cpuload_initialize_once();
@@ -185,6 +183,8 @@ int px4_platform_init()
 
 	uorb_start();
 
+	param_init();
+
 	px4_log_initialize();
 
 #if defined(CONFIG_SYSTEM_CDCACM) && defined(CONFIG_BUILD_FLAT)