dmaengine: edma: special case slot limit workaround

Currently drivers are limited to 19 slots for cyclic transfers.
However, if the DMA burst size is the same as the period size,
the period size can be changed to the full buffer size and
intermediate interrupts activated. Since intermediate interrupts
will trigger for each burst and the burst size is the same as
the period size, the driver will get interrupts each period as
expected. This has the benefit of allowing the functionality of
many more slots, but only uses 2 slots.

This workaround is only active if more than 19 slots are needed
and the burst size matches the period size.

Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>