dmaengine: edma: Document variables used for residue accounting

	int				cyclic;

	int				absync;

	int				pset_nr;

	struct edma_chan		*echan;

	int				processed;

	/*

	 * The following 4 elements are used for residue accounting.

	 *

	 * - processed_stat: the number of SG elements we have traversed

	 * so far to cover accounting. This is updated directly to processed

	 * during edma_callback and is always <= processed, because processed

	 * refers to the number of pending transfer (programmed to EDMA

	 * controller), where as processed_stat tracks number of transfers

	 * accounted for so far.

	 *

	 * - residue: The amount of bytes we have left to transfer for this desc

	 *

	 * - residue_stat: The residue in bytes of data we have covered

	 * so far for accounting. This is updated directly to residue

	 * during callbacks to keep it current.

	 *

	 * - sg_len: Tracks the length of the current intermediate transfer,

	 * this is required to update the residue during intermediate transfer

	 * completion callback.

	 */

	int				processed_stat;

	u32				residue;

	u32				sg_len;

	u32				residue;

	u32				residue_stat;

	struct edma_chan		*echan;

	struct edma_pset		pset[0];

};