ARM: vf610: use SMP_ON_UP for Vybrid SoC

The Vybrid SoC has only one Cortex-A5 core and hence should select
the SMP_ON_UP configuration on a SMP kernel.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>