Replace the atomic hrt_elapsed_time call with a non-atomic call

[LorenzMeier]

Almost nobody really need an atomic call to hrt_elapsed_time but lots of location in the code use the function as a convenience call. We should introduce an atomic option to reduce IRQ jitter and CPU load in the system.

[LorenzMeier]

Initial testing: We save ~1% CPU load with this on v5 (so about 2% CPU load on earlier hardware versions)

After fix (more CPU idle = better):

Current:

[dagar]

Is it easier to start from the other end and identify where hrt_elapsed_time in a critical section actually matters?

[LorenzMeier]

I did that already, and it's pretty much 0.1% of the calls needing this. Hence instead of inducing a massive diff I would switch those over.