cpu: Factor MaxInst(SrcDest)Regs out of the trace CPU.

cpu: Factor MaxInst(SrcDest)Regs out of the trace CPU.

Manage register and ROB dependencies using lists instead of arrays to
better support random removals, and avoid having to know the global
maximum number of registers in an instruction.

Change-Id: Ie9f30c61bac52ad31745a1011f62c95622908d2f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38386
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>