rcutorture: Set CONFIG_BOOTPARAM_HOTPLUG_CPU0 to offline CPU 0

There is now a BOOTPARAM_HOTPLUG_CPU0 Kconfig option that allows CPU 0
to be offlined on x86 systems.  This commit therefore sets this option in
the TREE01 rcutorture scenario in order to regularly test this capability.

Reported-by: "Zhang, Qiang1" <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>