configs,tests: Add tokens to GPU VIPER tester

configs,tests: Add tokens to GPU VIPER tester

This patch integrates tokens into the VIPER tester by adding a
GMTokenPort to the tester, having the tester acquire tokens for
requests that use tokens, and checking for available tokens
before issuing any requests.

Change-Id: Id317d703e4765dd5fa7de0d16f5eb595aab7096c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35135
Maintainer: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>