- 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

changed: "Mission rejected: land start required."
to: "Mission rejected: landing pattern required."

This new message is more clear to the average user.  When using RTL_TYPE = 1, mission feasibility checker adds the requirement of a landing sequence beginning with a MAV_CMD_DO_LAND_START and ending with a MAV_CMD_NAV_LAND with at least 1 other waypoint prior to the land waypoint.  The warning message "Mission rejected: land start required." is a common warning to trigger whenever the mission is blank or the mission is uploaded without a landing pattern.  The wording in this message confusing to the average user as they usually do not know the inner workings of the "landing pattern" that their planning software helps them make (e.g. Qgroundcontrol).  The only users who would know what a "Do_Land_Start" mission item is are advanced users already and this new message should work equally well for them as well as the non-advanced user.

changed: "Preflight Fail: Horizontal estimate Pos Error"
to: "Preflight Fail: Horizontal position estimate Error"

The comment description for COM_POS_FS_EPH incorrectly stated "...horizontal position error (EPV)...".  This fixes the acronym to "(EPH)".

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