fix: timings for MPM update due to faster F4 MCUs

[3djc]

Use proper timeout instead of MCU speed dependent loops

This fixes #5110

If confirmed solving the issue, needs to be cherry picked on main too

[pfeerick]

This doesn't fix the external MPM issue I'm seeing, and the MT12 (so another STM32F4 targe) with internal MPM flashes just fine with 2.10.0 (and this PR). 🤔 So I'm still thinking the issue may still somehow be T-Pro specific?

Also note, we cherry-pick from main into version branches generally, not the other way around (i.e. unless requested or is a version specific issue) ;)

[3djc]

This did fix it for me, and for the user reporting the issue (both on T Pro internal), and it is very logical that this loop is shorter on a faster MCU than the F2 is was designed with. It may be that the mpm is a tad slower on those or something similar.

As for your external MPM flash, it may be something else, but unfortunately I don't have one to reproduce

[pfeerick]

Oh, I'm not saying it doesn't make sense... it does... merely seems strange that neither TX16S or MT12, with internal MPMs, and Boxer with external MPM, all F4 MCUs, don't have any issue doing firmware updates without this change on 2.10 firmware... just concerned that there may be some additional factor not being considered here at play.

While the iRangeX 4in1 works fine, it won't update on TPro V2, and the RM 4in1 doesn't want to work at all with TProV2... which both update and work just fine with the Pocket, so it would seem there is something different for RM gear vs Jumper gear for external MPM. Plus, just tried TPro (not TProV2) with the RM 4in1, and that failed to update also, yet I've consistently been able to update both modules with the Pocket. The TPro was able to update it's internal MPM for what that is worth, running this PRs firmware so F2 was still working. 🤪 Everything was tested with 2.10 or 2.10.1 unless explicitly stated otherwise (like just now).

Having said that, this does resolve the issue at hand... and didn't break internal MPM flashing on TX16S, MT12 or TPro