spi_slave_queue_trans() function

Queue a SPI transaction for execution Queues a SPI transaction to be executed by this slave device. (The transaction queue size was specified when the slave device was initialised via spi_slave_initialize.) This function may block if the queue is full (depending on the ticks_to_wait parameter). No SPI operation is directly initiated by this function, the next queued transaction will happen when the master initiates a SPI transaction by pulling down CS and sending out clock signals. This function hands over ownership of the buffers in ``trans_desc`` to the SPI slave driver; the application is not to access this memory until ``spi_slave_queue_trans`` is called to hand ownership back to the application.