Revert "dmaengine: pxa_dma: add support for legacy transition"

This reverts commit c91134d9

.

The conversion of the pxa architecture is now finished for all
drivers, so this functions has fullfilled its purpose and can
now be removed.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>