mem: Implement and use the recvMemBackdoorReq func.

In the previous change, we miss some model supporting atomic backdoor.
We should also implement the recvMemBackdoorReq to them.

Change-Id: I4706d215aa4a5d18fe4306b2387f9c8750cb4b4a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66551
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