util-docker: Add gpu-fs to docker-compose.yaml

Though https://gem5-review.googlesource.com/c/public/gem5/+/59051 added
the gpu-fs image, it needs added to the docker-compose.yaml file to be
automatically build and pushed to our docker image repository.

With this patch a user can execute `docker-compose build gpu-fs` to
build this image locally.

Change-Id: Iacc768d3d1b7fccb8867e8c788012c292216cb02
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59349
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

util/dockerfiles/docker-compose.yaml

@@ -6,6 +6,11 @@ services:
             context: gcn-gpu
             dockerfile: Dockerfile
         image: gcr.io/gem5-test/gcn-gpu
+    gpu-fs:
+        build:
+            context: gcn-gpu
+            dockerfile: Dockerfile
+        image: gcr.io/gem5-test/gpu-fs
     sst:
         build:
             context: sst-11.1.0