POSIX: fixed hrt call and workqueue implementation

The HRT call processing normally happens via HW timer interrupt
handler. Since the POSIX port has no ISR handling, the HP work
queue is used.

Instead of irq_save() and irq_restore() calls to disable/enable
interrupts, a mutex is used to protect each queue.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/posix/px4_layer/px4_posix_impl.cpp

@@ -55,32 +55,20 @@ extern void hrt_init(void);
 
 __END_DECLS
 
-extern struct wqueue_s gwork[NWORKERS];
-
 namespace px4
 {
 
+void init_once(void);
+
+void init_once(void)
+{
+	work_queues_init();
+	hrt_init();
+}
+
 void init(int argc, char *argv[], const char *app_name)
 {
 	printf("App name: %s\n", app_name);
-
-	// Create high priority worker thread
-	g_work[HPWORK].pid = px4_task_spawn_cmd("wkr_high",
-			       SCHED_DEFAULT,
-			       SCHED_PRIORITY_MAX,
-			       2000,
-			       work_hpthread,
-			       (char* const*)NULL);
-
-	// Create low priority worker thread
-	g_work[LPWORK].pid = px4_task_spawn_cmd("wkr_low",
-			       SCHED_DEFAULT,
-			       SCHED_PRIORITY_MIN,
-			       2000,
-			       work_lpthread,
-			       (char* const*)NULL);
-
-	hrt_init();
 }
 
 }