clk: fixed-rate: Export driver parts for OF_PLATDATA_INST

We need to allow SoCs to create their own drivers for this so that they
can use their own of-platdata structs. To minimise code duplication,
export the driver operations and the ofdata_to_plat() setup function.

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