configs: Make GPU_VIPER config python3 friendly
configs: Make GPU_VIPER config python3 friendly

There is no xrange in python3. This will be required when eventually
20.2 is released.

Change-Id: I3a0da6353b70e6e17ce1f77d6177d48059e32487
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35855
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Maintainer: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5