scons: Use the os.path prefix when using components of that module.
scons: Use the os.path prefix when using components of that module.

That makes it obvious where the methods involved are coming from. Also
some of the imported names weren't being used.

Change-Id: I6ec75eef1e5ea9eae51e7df675e477dccb351bd1
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48126
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
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