ARM: dts: rockchip: add tsadc node for RV1108 SoC

Add tsadc needed main information for RV1108 SoC.
750000Hz is the max clock rate supported by tsadc module.

Signed-off-by: Rocky Hao <rocky.hao@rock-chips.com>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>