Changeset 7419 introduced a check for DOM0 before setting a bit in the

Changeset 7419 introduced a check for DOM0 before setting a bit in the
cpu_present map.  This prevents domU SMP kernels without HOTPLUG_CPU
support from booting.  Secondary cpus need to be present and online
before init/main.c:do_basic_setup() calls init_workqueues() (which
initializes per-cpu workqueues).

Without this patch, non HOTPLUG_CPU enabled kernels hang when flushing
cpu workqueues as the spinlock in the structure is never initialized (it
has a default value of zero which means the lock has been acquired on
x86).

Signed-off-by: Ryan Harper <ryanh@us.ibm.com>
Signed-off-by: Keir Fraser <keir@xensource.com>