drivers: ipm: Add support for NXP i.MX rev2 MU

With a number of the i.MX SoCs (e.g., the i.MX8M Plus), NXP has moved to
supporting the integrated Cortex-M cores with the MCUXpresso SDK (MCUX).
As a result, certain Zephyr drivers (such as the IPM driver) need to be
updated to utlize this new MCUX-based SDK.

This change adds support for the MCUX Messaging Unit driver pulled in by
this PR:
https://github.com/zephyrproject-rtos/hal_nxp/pull/130



Additionally, this change enables the new IPM_IMX_REV2 config for the
mimx8ml8_m7 SoC target which utilizes this new revision of the driver.

Signed-off-by: Chris Trowbridge <chris.trowbridge@lairdconnect.com>