dmaengine: cppi41: Move some constants to glue layer

Some constants are defined and use by the driver whereas they are
specifics to AM335x.
Add new variables to the glue layer, initialize them with the constants,
and use them in the driver.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>