ARM: ux500: Convert DT_MACHINE_START to use SMP operations

The Device Tree machine description for the ux5x0 was moved
recently and as a consequence missed the addition of SMP
operations. Without this patch SMP doesn't work and only one
CPU is present after booting.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>