AP_InertialSensor: BMI160: convert it to use Device periodic callback

Some notes:
 - The only place that made sense to use
   suspend_timer_procs()/resume_timer_procs() calls were where we registered
   the timer process. Now there's no need for that anymore. Remove those calls
   from other place in the source too.
 - There's no need to acquire the device lock now that we are running as a
   periodic callback.

libraries/AP_InertialSensor/AP_InertialSensor_BMI160.cpp

@@ -145,7 +145,6 @@ void AP_InertialSensor_BMI160::start()
 {
     bool r;
 
-    hal.scheduler->suspend_timer_procs();
     if (!_dev->get_semaphore()->take(100)) {
         AP_HAL::panic("BMI160: Unable to get semaphore");
     }
@@ -177,10 +176,9 @@ void AP_InertialSensor_BMI160::start()
     _accel_instance = _imu.register_accel(BMI160_ODR_TO_HZ(BMI160_ODR));
     _gyro_instance = _imu.register_gyro(BMI160_ODR_TO_HZ(BMI160_ODR));
 
-    hal.scheduler->register_timer_process(
-        FUNCTOR_BIND_MEMBER(&AP_InertialSensor_BMI160::_poll_data, void));
-
-    hal.scheduler->resume_timer_procs();
+    /* Call _poll_data() at 1kHz */
+    _dev->register_periodic_callback(1000,
+        FUNCTOR_BIND_MEMBER(&AP_InertialSensor_BMI160::_poll_data, bool));
 }
 
 bool AP_InertialSensor_BMI160::update()
@@ -407,15 +405,10 @@ read_fifo_end:
     }
 }
 
-void AP_InertialSensor_BMI160::_poll_data()
+bool AP_InertialSensor_BMI160::_poll_data()
 {
-    if (!_dev->get_semaphore()->take_nonblocking()) {
-        return;
-    }
-
     _read_fifo();
-
-    _dev->get_semaphore()->give();
+    return true;
 }
 
 bool AP_InertialSensor_BMI160::_hardware_init()
@@ -485,10 +478,7 @@ bool AP_InertialSensor_BMI160::_init()
     bool ret = false;
     _dev->set_read_flag(BMI160_READ_FLAG);
 
-    hal.scheduler->suspend_timer_procs();
     ret = _hardware_init();
-    hal.scheduler->resume_timer_procs();
-
     if (!ret) {
         hal.console->printf("BMI160: failed to init\n");
     }

libraries/AP_InertialSensor/AP_InertialSensor_BMI160.h

@@ -96,9 +96,9 @@ private:
     bool _configure_fifo();
 
     /**
-     * Timer routine to read data from the sensors.
+     * Device periodic callback to read data from the sensors.
      */
-    void _poll_data();
+    bool _poll_data();
 
     /**
      * Read samples from fifo.