rockchip: Use a separate clock ID for clocks

At present we use the same peripheral ID for clocks and pinctrl. While this
works it is probably better to use the device tree clock binding ID for
clocks. We can use the clk_get_by_index() function to find this.

Update the clock drivers and the code that uses them.

Signed-off-by: Simon Glass <sjg@chromium.org>