riscv: Add AMP support for the MPFS Discovery Kit board

[pmoussay-emdalo]

Description

This pull request aim to add AMP support for MPFS Discovery board. These changes have also been integrated in Yocto, please refer to polarfire-soc/meta-polarfire-soc-yocto-bsp#55

Type of change

• Add new DTS for AMP on Discovery kit

How Has This Been Tested?

• Test on MPFS Discovery board using linux AMP examples
• Test on MPFS Icicle Board using linux AMP examples

Test Configuration:

• Hardware: MPFS Discovery kit, Icicle Kit
• HSS version: Custom version (49059dbed), in order for the build to run the IHC bug must be fixed, make sure you have an HSS with that fix
• Buildroot / Yocto release: Add support for AMP to discovery kit meta-polarfire-soc-yocto-bsp#55

Checklist:

• I have reviewed my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have tested that my fix is effective or that my feature works
• I have added a maintainers file for any new board support