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

This function is only used once in the driver and uses some
intermediary variables that are not needed anymore. For this
reason it's been merged with 'imxdma_control'.

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>