ARM: mvebu: Implement the CPU hotplug support for the Armada 38x SoCs

ARM: mvebu: Implement the CPU hotplug support for the Armada 38x SoCs

This commit implements the CPU hotplug support for the Marvell Armada
38x platform. Similarly to what was done for the Armada XP, this
commit:

 * Implements the ->cpu_die() function of SMP operations by calling
   armada_38x_do_cpu_suspend() to enter the deep idle state for
   CPUs going offline.

 * Implements a dummy ->cpu_kill() function, simply needed for the
   kernel to know we have CPU hotplug support.

 * The mvebu_cortex_a9_boot_secondary() function makes sure to wake up
   the CPU if waiting in deep idle state by sending an IPI before
   deasserting the CPUs from reset. This is because
   mvebu_cortex_a9_boot_secondary() is now used in two different
   situations: for the initial boot of secondary CPUs (where CPU reset
   deassert is used to wake up CPUs) and for CPU hotplug (where an IPI
   is used to take CPU out of deep idle).

 * At boot time, we exit from the idle state in the
    ->smp_secondary_init() hook.

This commit has been tested using CPU hotplug through sysfs
(/sys/devices/system/cpu/cpuX/online) and using kexec.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1414669184-16785-5-git-send-email-gregory.clement@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>