dev: Introduce a reset() method on RegisterBank and Register classes.

This will make it much easier to implement reset behaviors on devices
which have RegisterBanks in them.

Change-Id: I73fe9874fcb69feed33611a320dcca85c0de2d0e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66671
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Yu-hsin Wang <yuhsingw@google.com>
Reviewed-by: Jui-min Lee <fcrh@google.com>
2 files changed