In general it makes not sense to hotplug out all the CPUs of a system, thus
ususally CPU0 is configured as not hot/plugggable.
Definitively, on a single core system it does not make sense to hotpolug out
the only available CPU.
This patch switch to usage of CPU1 for hotplug support probing, which is the
really first one for which enabling hotplug could be useful.
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>