torture: Allow 1G of memory for torture.sh kvfree testing

Yes, I do recall a time when 512MB of memory was a lot of mass storage,
much less main memory, but the rcuscale kvfree_rcu() testing invoked by
torture.sh can sometimes exceed it on large systems, resulting in OOM.
This commit therefore causes torture.sh to pase the "--memory 1G"
argument to kvm.sh to reserve a full gigabyte for this purpose.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>