arch-gcn3,python: Upgrade gpu_isa_parser.py to Python3
arch-gcn3,python: Upgrade gpu_isa_parser.py to Python3

Change-Id: I0a37809589d3796f7c74614a337cc690aae6c9a0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47021
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Reviewed-by: Matthew Poremba <f1eb50f3368ce197c52b19f7fdb5aa7a278f15fd@amd.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