ARM: imx51: Configure M4IF to avoid visual artifacts

Configure the M4IF registers as per the vendor bootloader
to avoid visual artifacts during video playback.

This way we don't need to rely on the bootloader configuration for
optimal IPU/VPU bus priorities.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Sergey Lapin <sergey.lapin@cogentembedded.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>