cpu: Refactor of Physical Register implementation

cpu: Refactor of Physical Register implementation

The implementation of the PhyRegId class is shared between multiple
cpu models. The o3/misc.hh should only be included in o3 models.

This patch removes the dependencies between different model
implementations, allowing to add new O3-like CPU model.

Change-Id: Ibb812517043befe75c48fab3ce9605a0d272870b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/16908
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Bradley Wang <radwang@ucdavis.edu>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>