mem: add clear modifiers for request flags

During the memory requests, it's possible some control attribute
changed by IPs. There are three ways to model the behavior.

1. Modify the flags of current request, but there's no way to unset
   the attribute now.
2. Clone the request with original flags, but there's no way to unset the
   attribute.
3. Clone the request with zero flags, but it will ask the model to review
   all the flags and set individually.

To preserve the original requests, we may pick the second approach. It's
still good to have clear modifiers to make the modeling more easier by
modifying the cloned request.

Change-Id: Ib216ca20c79b0f84be15ed4b0ec00354a428bac9
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59809
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed