dt-bindings: timer: rockchip: Add rockchip,rk3128-timer

Add rockchip,rk3128-timer compatible string.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Link: https://lore.kernel.org/r/0e57f38f-bace-8556-7258-aa0b3c0ac103@gmail.com