davinci: EDMA: add support for dm646x

Enables module clock for DM646x EDMA channel controller and transfer
controller.

Signed-off-by: Naresh Medisetty <naresh@ti.com>
Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>