ARM: dts: rockchip: Pass the 'clock-latency' property on rv1108

Like it is done on cpu nodes of other Rockchip SoCs, pass the
'clock-latency' property to the CPU node, so that cpufreq driver
can take the latency into account when switching frequencies.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>