configs: Generalize FileSystemConfig for non se.py

This patch updates the FileSystemConfig so it works with more kinds of
config scripts (e.g., the Learning gem5 scripts).

There are 4 main changes:
- Added system as a parameter to the config_filesystem function so the
function can search the system for the number of CPUs instead of relying
on options from Options.py
- Instead of calling redirect_paths everywhere config_filesystem is
used, now it is implicitly called.
- Cleaned up the Ruby scripts a bit to remove redundant calls to
config_filesystem
- Added a config_filesystem call to the Ruby Learning gem5 script
(currently the only Learning gem5 script that requires it).

In the future, I think it would be better to move the config_filesystem
call into simulate.py, probably into the instantiate function. I tried to
use the per-CPU configuration parameters instead of options from
Options.py, but that's not possible until after the SimObject params
have been finalized in instantiate.

Change-Id: Ie6501a7435cfb3ac9d2b45be3722388b34063b1e
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18848
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>

configs/example/se.py

@@ -64,7 +64,7 @@ from common import CacheConfig
 from common import CpuConfig
 from common import BPConfig
 from common import MemConfig
-from common.FileSystemConfig import redirect_paths, config_filesystem
+from common.FileSystemConfig import config_filesystem
 from common.Caches import *
 from common.cpu2000 import *
 
@@ -246,9 +246,6 @@ for i in range(np):
 
     system.cpu[i].createThreads()
 
-system.redirect_paths = redirect_paths(os.path.expanduser(options.chroot))
-config_filesystem(options)
-
 if options.ruby:
     Ruby.create_system(options, False, system)
     assert(options.num_cpus == len(system.ruby._cpu_ports))
@@ -278,6 +275,7 @@ else:
     system.system_port = system.membus.slave
     CacheConfig.config_cache(options, system)
     MemConfig.config_mem(options, system)
+    config_filesystem(system, options)
 
 root = Root(full_system = False, system = system)
 Simulation.run(options, root, system, FutureClass)