Only expose up_pwm_update for onshot

This api will REWORD

src/drivers/drv_pwm_output.h

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2012-2015 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2012-2015, 2017 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -305,9 +305,6 @@ struct pwm_output_rc_config {
  * This is the low-level API to the platform-specific PWM driver.
  */
 
-__EXPORT extern void up_pwm_set_oneshot_mode(bool on);
-__EXPORT extern bool up_pwm_get_oneshot_mode(void);
-
 /**
  * Intialise the PWM servo outputs using the specified configuration.
  *
@@ -364,11 +361,12 @@ __EXPORT extern uint32_t up_pwm_servo_get_rate_group(unsigned group);
 __EXPORT extern int	up_pwm_servo_set_rate_group_update(unsigned group, unsigned rate);
 
 /**
- * Force update of all timer channels in group.
+ * Trigger all timer's channels in Oneshot mode to fire
+ * the oneshot with updated values.
+ * Nothing is none if not in onshot mode.
  *
- * @param group		The rate group to update.
  */
-__EXPORT extern void up_pwm_force_update(void);
+__EXPORT extern void up_pwm_update(void);
 
 /**
  * Set the current output value for a channel.