ARM: SoC: convert highbank to SMP operations

Convert the highbank platform to use struct smp_operations to provide
its SMP and CPU hotplug operations.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>