ARM: highbank: fix secondary boot and hotplug

With commit 384a2902

 (ARM: gic: use a private mapping for CPU target
interfaces), wake-up IPIs now go to all cores as the gic cpu interface
numbering may not follow core numbering. This broke secondary boot on
highbank since the boot address was already set for all secondary cores,
this caused all cores to boot before the kernel was ready.

Fix this by moving the setting of the jump address to
highbank_boot_secondary instead of highbank_smp_prepare_cpus and
highbank_cpu_die. Also, clear the address when we boot. This prevents
cores from booting before they are actually triggered and is also necessary
to get suspend/resume to work.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>