config, sim-se: bugfix for 54c77aa0

config, sim-se: bugfix for 54c77aa0

The NULL ISA does not have some members for the options
class which are referenced by the FileSystemConfig
code.

Create default values for the members so that the
simulation does not fail during the configuration phase.

Change-Id: Ie65bf0e5550c964eae42d1df4c36c2c5bc4ea703
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18748
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>