dt-bindings: timer: Simplify conditional expressions

The sun4i timer IP block has a variable number of interrupts based on
the compatible. Use enums to combine the two sections for the existing
3-interrupt variants, and to simplify adding new compatible strings.

Acked-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210322044707.19479-2-samuel@sholland.org