Add a device-tree source for petalogix-s3adsp1800 and
recompile the DTB.

This also removes the unused mpmc node which causes
compilation warnings.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>