gpu-compute: Add methods to read GPU memory requestor ID

These methods are called from various places to override the requestor
ID of a request in order to determine which Ruby network a request
should be routed on.

Change-Id: Ic0270ddd7123f0457a13144e69ef9132204d4334
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57651
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
6 files changed