config: Make configs/common a Python package

Continue along the same line as the recent patch that made the
Ruby-related config scripts Python packages and make also the
configs/common directory a package.

All affected config scripts are updated (hopefully).

Note that this change makes it apparent that the current organisation
and naming of the config directory and its subdirectories is rather
chaotic. We mix scripts that are directly invoked with scripts that
merely contain convenience functions. While it is not addressed in
this patch we should follow up with a re-organisation of the
config structure, and renaming of some of the packages.

configs/learning_gem5/part1/caches.py

@@ -36,7 +36,7 @@ line options from each individual class.
 
 from m5.objects import Cache
 
-import SimpleOpts
+from common import SimpleOpts
 
 # Some specific options for caches
 # For all options see src/mem/cache/BaseCache.py

configs/learning_gem5/part1/two_level.py

@@ -46,13 +46,13 @@ import m5
 from m5.objects import *
 
 # Add the common scripts to our path
-m5.util.addToPath('../../common')
+m5.util.addToPath('../../')
 
 # import the caches which we made
 from caches import *
 
 # import the SimpleOpts module
-import SimpleOpts
+from common import SimpleOpts
 
 # Set the usage message to display
 SimpleOpts.set_usage("usage: %prog [options] <binary to execute>")