dmaengine: add context parameter to prep_slave_sg and prep_dma_cyclic

Add context parameter to device_prep_slave_sg() and device_prep_dma_cyclic()
interfaces to allow passing client/target specific information associated
with the data transfer.
Modify all affected DMA engine drivers.

Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>