arm64: dts: rockchip: Add cif test clocks for rk3399

There are three pins can act as cif test clock for rk3399.
They're sourced from 24M and output 24M by default and some boards
may use them as camera 24M xvclk.

Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>