ARM: mvebu: use CPU_METHOD_OF_DECLARE for SMP on Armada XP

This commit adds the CPU_METHOD_OF_DECLARE declaration for the Armada
XP SMP operations. Note that the .smp_ops field of Armada XP
DT_MACHINE structure is kept, in order to ensure we remain compatible
with older Device Trees that do not include the "enable-method"
property for the CPUs.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1397483648-26611-3-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>