net: davinci_emac: cleanup unused cpdma code

Having switched over to the newly introduced cpdma layer, this patch now
removes a whole bunch of code that is now unused.  This patch has been
maintained separate strictly for reasons of readability.
Signed-off-by: NCyril Chemparathy <cyril@ti.com>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Tested-by: NMichael Williamson <michael.williamson@criticallink.com>
Tested-by: NCaglar Akyuz <caglarakyuz@gmail.com>
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>