Add the X2.1 bootloader boardID as a FMUv3 target

Please add the X2.1 bootloader to be recognized as a FMUv3 in Mission Planner for purposes of uploading firmware.

Here is what Mission Planner reports when it detects the X2.1 - INFO MissionPlanner.Utilities.Firmware - Found board type 33 boardrev 0 bl rev 5 fwmax 2080768 on COM8

Please let me know if any further information is needed?

Thank you in advance!

Search Mission Planner for the board-ID and FMUv3 recognition logic, using board type 33, boardrev 0, and bootloader revision 5 as the starting values. Verify that the X2.1 is recognized as FMUv3 and that firmware upload handling reaches the expected target.

Written by the indexing model from the issue text.