misc,configs: Add gitignore for downloaded files
misc,configs: Add gitignore for downloaded files

Change-Id: Idf9aa0e5e3b8490d1e75c8811a8dfad48bbdada3
Signed-off-by: Jason Lowe-Power <68c46a606457643eab92053c1c05574abb26f861@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49434
Reviewed-by: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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