arch,cpu: Use PCStateBase in buildRetPC.

Change-Id: I9d9f5b25613440737b1d67134fcae09aa68baf8b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52044
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
8 files changed