dt-bindings: freescale: Add bindings for the M4IF module

Add bindings for the M4IF module present on i.MX51.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>