The previous code used the numeric baudrate as the speed argument
for cfsetispeed() and cfsetospeed(). This works in OSX and NuttX,
but is not portable.

This fix introduces a new method to convert baudrate to speed using
constants such as B115200.

Signed-off-by: Gabriel Moreno <gabrielm@cs.cmu.edu>

mc_pos_control - reduce smooth_velocity_takeoff default threshold, set initial takeoff speed to 0 and remove useless else

PositionControl - use dynamic constraints to saturate velocity controller for now as it is needed for the current smooth takeoff logic. Will be reverted after smooth takeoff refactor

Position Controller - Saturate the controllers using static parameters. Handle saturations in the flight tasks only

Manual vel smooth - use speed_up and speed_down constraints to limit velocity target of the trajectory generator

 - also applies to mission_stats_entry_s, mission_fence_point_s,
   mission_save_point_s
 - -Wpadded warning is disabled by default because the snapdragon
   toolchain doesn't respect the pragma pop

Fixes regression from https://github.com/PX4/Firmware/pull/11216.

 - Remove a constructor overload by adding default values, and disambiguate a few variables by adding verbosity to naming. 

 - see 1259864 Data corruption in a sequence of Write-Through stores and loads
 - if we can be certain this sequence won't occur in PX4 then the d-cache will be re-enabled