dt-bindings: pwm: allwinner,sun4i-a10-pwm: add top-level constraints

dt-bindings: pwm: allwinner,sun4i-a10-pwm: add top-level constraints

Properties with variable number of items per each device are expected to
have widest constraints in top-level "properties:" block and further
customized (narrowed) in "if:then:".  Add missing top-level constraints
for clock-names.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20240818172828.121728-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>