MIPS: jz4740: Remove custom DMA API

Now that all users of the custom jz4740 DMA API have been converted to use
the dmaengine API instead we can remove the custom API and move all the code
talking to the hardware to the dmaengine driver.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>