clk: rockchip: use separate compatibles for rk3288w-cru

Commit 1627f683 ("clk: rockchip: Handle clock tree for rk3288w variant")
added the check for rk3288w-specific clock-tree changes but in turn would
require a double-compatible due to re-using the main rockchip,rk3288-cru
compatible as entry point.

The binding change actually describes the compatibles as one or the other
so adapt the code accordingly and add a real second entry-point for the
clock controller.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # rock-pi-n8
Link: https://lore.kernel.org/r/20200703154948.260369-1-heiko@sntech.de