dmaengine: add TI EDMA DMA engine driver

Add a DMA engine driver for the TI EDMA controller. This driver
is implemented as a wrapper around the existing DaVinci private
DMA implementation. This approach allows for incremental conversion
of each peripheral driver to the DMA engine API. The EDMA driver
supports slave transfers but does not yet support cyclic transfers.

Signed-off-by: Matt Porter <mporter@ti.com>
Tested-by: Tom Rini <trini@ti.com>
Tested-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>