spi: dt-bindings: qup: Document interconnects

When the SPI QUP controller is used together with a DMA engine it needs
to vote for the interconnect path to the DRAM. Otherwise it may be
unable to access the memory quickly enough.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Link: https://lore.kernel.org/r/20230919-spi-qup-dvfs-v2-3-1bac2e9ab8db@kernkonzept.com


Signed-off-by: Mark Brown <broonie@kernel.org>