tests: Migrated 80.dram scons-based tests to testlib framework

tests: Migrated 80.dram scons-based tests to testlib framework

"configs/dram/low_power_sweep.py" has been modified to keep the
generated "lowp_sweep.cfg" file in "configs/dram". This generated file
is now ignored by git.

Change-Id: I700d04944fee58f8a506c71fd474b84024ec4374
Jira: https://gem5.atlassian.net/browse/GEM5-109
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25923
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>