clk: rockchip: include rk3228 downstream muxes into fractional dividers

During the initial conversion to the newly introduced combined fractional
dividers+muxes the rk3228 clocks were left out, so convert them now.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>