move: rockchip: move clock drivers into a subdirectory

move: rockchip: move clock drivers into a subdirectory

With the number of Rockchip clock drivers increasing, don't clutter up
the core drivers/clk directory with them and instead move them out of
the way into a separate subdirectory.

Suggested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Simon Glass <sjg@chromium.org>
Updated for rk3399:
Signed-off-by: Simon Glass <sjg@chromium.org>