fastmodel: Add CortexA76 model reset port

The model reset is an aggregated logic to reset the whole model. The
port helps us to simulate the reboot process.

Change-Id: I9aacc398b299e26e4675f7229db1afc8f6c8a34f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58814
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
4 files changed