dt-bindings: timer: rockchip: Add rk3576 compatible

Add compatible string for Rockchip RK3576 timer.

Signed-off-by: Detlev Casanova <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Heiko Stuebner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Daniel Lezcano <[e-mail]>

Documentation/devicetree/bindings/timer/rockchip,rk-timer.yaml

···
               - rockchip,rk3228-timer
               - rockchip,rk3229-timer
               - rockchip,rk3368-timer
+              - rockchip,rk3576-timer
               - rockchip,rk3588-timer
               - rockchip,px30-timer
           - const: rockchip,rk3288-timer