Removed extra abstracton layer in systemlib

The calls to task_spawn_cmd, kill_all, and systemreset  were wrappers
around the px4_{task_spawn_cmd|kill_all|systemreset} implementations.

Removed the wrappers and changed all calls to the px4_ equivalents.

NuttX specific code was moved into px4_tasks.h

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

src/examples/matlab_csv_serial/matlab_csv_serial.c

@@ -87,7 +87,7 @@ static void usage(const char *reason)
  * Makefile does only apply to this management task.
  *
  * The actual stack size should be set in the call
- * to task_spawn_cmd().
+ * to px4_px4_task_spawn_cmd().
  */
 int matlab_csv_serial_main(int argc, char *argv[])
 {
@@ -103,7 +103,7 @@ int matlab_csv_serial_main(int argc, char *argv[])
 		}
 
 		thread_should_exit = false;
-		daemon_task = task_spawn_cmd("matlab_csv_serial",
+		daemon_task = px4_px4_task_spawn_cmd("matlab_csv_serial",
 					     SCHED_DEFAULT,
 					     SCHED_PRIORITY_MAX - 5,
 					     2000,