drivers/tone_alarm and tune_control small improvements/cleanup

- drivers/tone_alarm: move to ModuleBase and purge CDev (/dev/tone_alarm0)
 - drivers/tone_alarm: only run on tune_control publication (or scheduled note) rather than continuously
 - drivers/tone_alarm: use HRT to schedule tone stop (prevents potential disruption)
 - msg/tune_control: add tune_id numbering
 - systemcmds/tune_control: add "error" special case tune_id
 - move all tune_control publication to new uORB::PublicationQueued<>
 - start tone_alarm immediately after board defaults are loaded to fix potential startup issues
 - for SITL (or other boards with no TONE output) print common messages (startup, error, etc)

platforms/common/include/px4_platform_common/px4_work_queue/ScheduledWorkItem.hpp

@@ -44,6 +44,8 @@ class ScheduledWorkItem : public WorkItem
 {
 public:
 
+	bool Scheduled() { return !hrt_called(&_call); }
+
 	/**
 	 * Schedule next run with a delay in microseconds.
 	 *
@@ -59,6 +61,13 @@ public:
 	 */
 	void ScheduleOnInterval(uint32_t interval_us, uint32_t delay_us = 0);
 
+	/**
+	 * Schedule next run at a specific time.
+	 *
+	 * @param time_us		The time in microseconds.
+	 */
+	void ScheduleAt(hrt_abstime time_us);
+
 	/**
 	 * Clear any scheduled work.
 	 */

platforms/common/px4_work_queue/ScheduledWorkItem.cpp

@@ -57,6 +57,11 @@ void ScheduledWorkItem::ScheduleOnInterval(uint32_t interval_us, uint32_t delay_
 	hrt_call_every(&_call, delay_us, interval_us, (hrt_callout)&ScheduledWorkItem::schedule_trampoline, this);
 }
 
+void ScheduledWorkItem::ScheduleAt(hrt_abstime time_us)
+{
+	hrt_call_at(&_call, time_us, (hrt_callout)&ScheduledWorkItem::schedule_trampoline, this);
+}
+
 void ScheduledWorkItem::ScheduleClear()
 {
 	// first clear any scheduled hrt call, then remove the item from the runnable queue