arch: Add a newPCState method to the ISA class.

This method is the seed which creates a new PCState object of the
appropriate type. It can be used to initialize PCStateBase *s so that they
always point to something valid and can be manipulated without having to
first check if there's something there, as opposed to the alternative
where a pointer might be null until it's first pointed at something.

Change-Id: If06ee633846603acbfd2432f3d8bac6746a8b729
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52040
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
8 files changed