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/work_queue.c

@@ -43,7 +43,10 @@
 #include <signal.h>
 #include <stdint.h>
 #include <queue.h>
+#include <stdio.h>
+#include <semaphore.h>
 #include <px4_workqueue.h>
+#include "work_lock.h"
 
 #ifdef CONFIG_SCHED_WORKQUEUE
 
@@ -117,13 +120,13 @@ int work_queue(int qid, struct work_s *work, worker_t worker, void *arg, uint32_
    * from with task logic or interrupt handlers.
    */
 
-  //flags        = irqsave();
+  work_lock(qid);
   work->qtime  = clock_systimer(); /* Time work queued */
 
   dq_addlast((dq_entry_t *)work, &wqueue->q);
   px4_task_kill(wqueue->pid, SIGCONT);      /* Wake up the worker thread */
 
-  //irqrestore(flags);
+  work_unlock(qid);
   return PX4_OK;
 }