resources: Fixed image URLs to point to img.gz

In efforts to reduce our storage costs. The gem5 images have been
compressed using GZIP. This patch alters the URLs to point towards these
gzipped image files.

We've also added the .img extension to make it clearer as to what these
files are.

Change-Id: I1480f4248619b601f6fabab6596623c086103e4b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/35121
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
4 files changed
tree: 2c83e650b7fa4c40ab69b07b87d72810edcc1dc2
  1. src/
  2. README.md