ARM: SMP: use a timing out completion for cpu hotplug

    ARM: SMP: use a timing out completion for cpu hotplug

    Rather than open-coding the jiffy-based wait, and polling for the
    secondary CPU to come online, use a completion instead.  This
    removes the need to poll, instead we will be notified when the
    secondary CPU has initialized.

    Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>