Check the MX51 chip revision in run-time so that the correct SDMA firmware can
be loaded.

While at it also remove the silicon revision from the sdma_script_start_addrs
structure name for MX51. All the MX51 revisions share the same SDMA start addresses.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>