clk: rockchip: Add CLK_SET_RATE_PARENT to sclk_uart clocks

We'd like to be able to set the clock rate of the sclk_uart clocks and
actually be able to achieve clock rates greater than 24MHz.  To do
this we need to be able to pass rate changes upward.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>