ARM: dts: Fill in CPU clock-frequency for exynos5410

It's 1.6 GHz for the Cortex-A15.

Avoids warnings like "/cpus/cpu@0 missing clock-frequency property".

Signed-off-by: Andreas Faerber <afaerber@suse.de>
Reviewed-by: Tarek Dakhran <t.dakhran@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>