AP_Vehicle: separate gyrofft gyro sampling from fft initiation

move FFT gyro sampling into fast loop for all vehicles
rename FFT update method

libraries/AP_Vehicle/AP_Vehicle.cpp

@@ -113,6 +113,16 @@ void AP_Vehicle::loop()
     G_Dt = scheduler.get_loop_period_s();
 }
 
+/*
+ fast loop callback for all vehicles. This will get called at the end of any vehicle-specific fast loop.
+ */
+void AP_Vehicle::fast_loop()
+{
+#if HAL_GYROFFT_ENABLED
+    gyro_fft.sample_gyros();
+#endif
+}
+
 /*
   common scheduler table for fast CPUs - all common vehicle tasks
   should be listed here, along with how often they should be called (in hz)
@@ -123,7 +133,7 @@ const AP_Scheduler::Task AP_Vehicle::scheduler_tasks[] = {
     SCHED_TASK_CLASS(AP_RunCam,    &vehicle.runcam,         update,                   50, 50),
 #endif
 #if HAL_GYROFFT_ENABLED
-    SCHED_TASK_CLASS(AP_GyroFFT,   &vehicle.gyro_fft,       sample_gyros,      LOOP_RATE, 50),
+    SCHED_TASK_CLASS(AP_GyroFFT,   &vehicle.gyro_fft,       update,                  400, 50),
     SCHED_TASK_CLASS(AP_GyroFFT,   &vehicle.gyro_fft,       update_parameters,         1, 50),
 #endif
     SCHED_TASK(send_watchdog_reset_statustext,         0.1,     20),

libraries/AP_Vehicle/AP_Vehicle.h

@@ -190,7 +190,7 @@ protected:
 
     // main loop scheduler
     AP_Scheduler scheduler{FUNCTOR_BIND_MEMBER(&AP_Vehicle::fast_loop, void)};
-    virtual void fast_loop() { }
+    virtual void fast_loop();
 
     // IMU variables
     // Integration time; time last loop took to run