The i.MX Messaging Unit is a two side block which allows applications
implement communication over this sides.

The MU includes the following features:
- Messaging control by interrupts or by polling
- Four general-purpose interrupt requests reflected to the other side
- Three general-purpose flags reflected to the other side
- Four receive registers with maskable interrupt
- Four transmit registers with maskable interrupt
Reviewed-by: NVladimir Zapolskiy <vz@mleia.com>
Reviewed-by: NDong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: NOleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>