dmaengine: imx-sdma: pass sdma firmware name via platform data

It is not good to have cpu_name and to_version encoded into sdma
firmware name as variables.  For example, there are three TOs of
imx51 soc, the sdma script never changes since TO1, which means
all three TOs of imx51 uses TO1 version of sdma script.  But we
have to prepare three identical firmwares, sdma-imx51-to1.bin
sdma-imx51-to2.bin and sdma-imx51-to3.bin, to have the kernel
capable of running on all three TOs.

The patch removes cpu_name and to_version from sdma platform data,
and instead uses fw_name to pass the firmware name, so that we can
pass the TO version where it's relevant and skip it where only one
firmware exists.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>