util: Use a dispatch table to call ops in the m5 utility.

This way different implementations can be substituted in depending on
how the low level ops should actually be triggered (inst, addr,
semihosting, (etc?)).

Change-Id: I7c6eab7d87cc973d0bc9c1889037a0f89ce057e8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27238
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
2 files changed