mem: Add system request flag for dGPUs
mem: Add system request flag for dGPUs

dGPUs can translate a virtual address and will not know if the address
resides in system/host memory or device/dGPU memory until the
translation is complete. In order to mark requests as going to either
system memory or device memory we add a field to the Request class.

Change-Id: Ib1e80e8d03ecdfeb11c24d979ccc4b912ce07f91
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51852
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Maintainer: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>

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