Enable MU for HiFi4 DSP from i.MX8M Plus

[iuliana-prodan]

Prerequisites

• I have checked latest main branch and the issue still exists.
• I did not see it is stated as known-issue in release notes.
• No similar GitHub issue is related to this change.
• My code follows the commit guidelines of this project.
• I have performed a self-review of my own code.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.

Describe the pull request
Add MU support for HiFi4 DSP from i.MX8 M Plus target.
This is used for IPC.
Having this enabled we can run the openamp_rsc_table sample from Zephyr: https://github.com/zephyrproject-rtos/zephyr/tree/main/samples/subsys/ipc/openamp_rsc_table

Type of change
Enable MU for DSP

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Tests

• Test configuration (please complete the following information):

  • Hardware setting: DSP from i.MX8MP
  • Toolchain: gcc

• Test executed
  Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

  • Build Test
    Build Zephyr sample openamp_rsc_table for nxp_adsp_imx8m board
  • Run Test
    Run Zephyr sample openamp_rsc_table and the output will be displayed on console.

[iuliana-prodan]

Hi @dleach02, @mmahadevan108, @mcuxsusan
Can you, please, help review this?

[iuliana-prodan]

@mcuxsusan can you please help me with a review?

[iuliana-prodan]

cc: @jasonNXP @zejiang0jason