dt-bindings: timer: Add Allwinner suniv timer

Add compatible string for Allwinner suniv timer which is similar to
sun4i timer.

Signed-off-by: Mesih Kilinc <mesihkilinc@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>