dmaengine: imx-dma: remove 'imxdma_setup_mem2mem_hw' function.

This function is only used once in the driver and has a lot of checks
that are not needed anymore. For this reason it's been merged
with 'imxdma_enable_hw'.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>