arch,cpu: Move the inUserMode function to the ISA object.

This function is used when tracing execution with --debug-flags=Exec.
The data used by the function (now method) is stored in the ISA object,
and so that's a logical place to move it.

Change-Id: I624f9365124679343e988cabfb4e1929225b439a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39323
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
15 files changed