arm64: dts: rockchip: add tsadc node for rk3328 SoC

add tsadc needed main information for rk3328 SoC.
50000Hz is the max clock rate supported by tsadc module.

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