kern: Stop using a pseudo instruction to quiesce the ThreadContext.

kern: Stop using a pseudo instruction to quiesce the ThreadContext.

The pseudo instruction implementation is very short, and so doing the
work it was doing directly doesn't really add much to the
implementation of the udelay events. By not calling the pseudo
instruction we also uncouple these unrelated mechanisms and don't,
for instance, cause pseudo instruction debug output every time udelay
executes.

Change-Id: I5c9b32509562487e53b2acfa1a3f6226d33d1cfd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23748
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Gabe Black <gabeblack@google.com>