sim-se: Use CONFIG_CLONE_BACKWARDS for Arm

sim-se: Use CONFIG_CLONE_BACKWARDS for Arm

Linxu on Arm users the CLONE_BACKWARDS argument order for the clone
syscall.

Change-Id: I48deb4f03140c9d4ef7a89e3e33813e76777f999
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Cc: Giacomo Travaglini <giacomo.travaglini@arm.com>
Cc: Javier Setoain <javier.setoain@arm.com>
Cc: Brandon Potter <Brandon.Potter@amd.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15416
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>