dt-bindings: arm-smmu: disallow clocks when not used

Disallow clocks for variants other than:
1. SMMUs with platform-specific compatibles which list explicit clocks
   and clock-names,
2. SMMUs using only generic compatibles, e.g. arm,mmu-500, which have a
   variable clocks on different implementations.

This requires such variants with platform-specific compatible, to
explicitly list the clocks or omit them, making the binding more
constraint.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221222092355.74586-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Will Deacon <will@kernel.org>