ARM: davinci/common: Convert edma driver to handle one eDMA instance per driver

Currently we have one device created to handle all (maximum 2) eDMAs in the
system.
With this change all eDMA instance will have it's own device/driver.
This change is needed for further cleanups in the eDMA driver stack since
the one device/driver to handle all eDMAs in the system was not flexible
enough and prevents the upcoming work.

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