configs: Add root redirect path in SE mode only when set

configs: Add root redirect path in SE mode only when set

As it is now, the default behaviour, if chroot is not specified, is to
add a redirect path which is simply mappping "/" in guest to "/" in
host.  This patch avoids this unnecessary mapping, and adds a redirect
path to root only if chroot is specified.

Change-Id: Icbe863887330d7071e0005333b408ffc8cad41d6
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23064
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>