arm64: dts: qcom: sdm630: move DSI opp-table into DSI node

The soc node is supposed to have only device nodes with MMIO addresses,
so move the DSI OPP into the DSI controller node to fix:

  sda660-inforce-ifc6560.dtb: soc: opp-table-dsi: {'compatible': ['operating-points-v2'], ... should not be valid under {'type': 'object'}
    From schema: dtschema/schemas/simple-bus.yaml

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230324202244.744271-5-krzysztof.kozlowski@linaro.org