espressif: busio.SPI: Use SPI_DMA_CH_AUTO
espressif: busio.SPI: Use SPI_DMA_CH_AUTO

All 3 micros we care about (S2, S3, C3) state in the documentation
that DMA channel can be specified as SPI_DMA_CH_AUTO.

Specifying a specific DMA channel explicitly doesn't _ever_ work on
ESP32-S3, so no SPI bus could be used.

Testing performed: On the ESP32-S3-DevKitC, used neopixel_spi to
turn the onboard neopixel red, green, and blue

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