dw_dmac: add cyclic API to DW DMA driver

This patch adds a cyclic DMA interface to the DW DMA driver. This is
very useful if you want to use the DMA controller in combination with a
sound device which uses cyclic buffers.

Using a DMA channel for cyclic DMA will disable the possibility to use
it as a normal DMA engine until the user calls the cyclic free function
on the DMA channel. Also a cyclic DMA list can not be prepared if the
channel is already active.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Acked-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Acked-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>