vtol_att_control: consolidated standard parameters & fix usage of hrt_elapsed time

- standard vtol was implementing many custom parameters although they
are generic and should be shared between the vtol types
- removed heavy usage of hrt_elapsed_time() which is a system call and
could be computationally expensive

src/modules/vtol_att_control/standard_params.c

@@ -39,16 +39,6 @@
  * @author Roman Bapst	<roman@px4.io>
  */
 
-/**
- * Target throttle value for pusher/puller motor during the transition to fw mode
- *
- * @min 0.0
- * @max 1.0
- * @increment 0.01
- * @decimal 3
- * @group VTOL Attitude Control
- */
-PARAM_DEFINE_FLOAT(VT_TRANS_THR, 0.6f);
 
 /**
  * Maximum allowed down-pitch the controller is able to demand. This prevents large, negative
@@ -113,14 +103,12 @@ PARAM_DEFINE_FLOAT(VT_B_REV_OUT, 0.0f);
 PARAM_DEFINE_FLOAT(VT_B_REV_DEL, 0.0f);
 
 /**
- * Thottle output during back transition
- * For ESCs and mixers that support reverse thrust on low PWM values set this to a negative value to apply active breaking
- * For ESCs that support thrust reversal with a control channel please set VT_B_REV_OUT and set this to a positive value to apply active breaking
+ * Defines the time window during which the pusher throttle will be ramped up linearly to VT_F_TRANS_THR during a transition
+ * to fixed wing mode. Zero or negative values will produce an instant throttle rise to VT_F_TRANS_THR.
  *
- * @min -1
- * @max 1
+ * @max 20
  * @increment 0.01
  * @decimal 2
  * @group VTOL Attitude Control
  */
-PARAM_DEFINE_FLOAT(VT_B_TRANS_THR, 0.0f);
+PARAM_DEFINE_FLOAT(VT_PSHER_RMP_DT, 3.0f);