tests: Add tests for DRAM low power modes

This patch adds two regression tests that execute the script in the
configs dir for triggering low power mode transitions. A separate
test is required for each page policy because for close-adaptive
page policy the DRAM goes into the Precharge Power-down mode while
for open-adaptive page policy it goes into the Activate Power-down
mode.

Change-Id: Iad61af23f132db046f2857cc3ef64b2bf42cf5e4
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5726
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

configs/dram/low_power_sweep.py

@@ -43,7 +43,7 @@ from m5.objects import *
 from m5.util import addToPath
 from m5.stats import periodicStatDump
 
-addToPath('../common')
+addToPath(os.getcwd() + '/configs/common')
 import MemConfig
 
 # This script aims at triggering low power state transitions in the DRAM