Update Xtensa FreeRTOS support to v11

[ianstcdns]

Bring Xtensa port up to date with FreeRTOS version 11, moving to Partner-Supported-Ports submodule.

Description

Bring existing Cadence-maintained Xtensa v10.4.4-stable port up to date in the FreeRTOS v11 context:

• Incorporate and consolidate all existing Xtensa port bug-fixes from internal, external, and third-party repositories
• Additional improvements in tickless-idle support, newlib, overlays, coprocessor management, and NX MPU and syscall handling.
• Maintain consistent formatting, copyright, and whitespace
• Update Xtensa port sub-version to 3.0.0

Test Steps

• Tested via various demo and stress tests as provided through the Partner-Supported-Demos submodule.
• Regression testing on many different LX7, LX8, and NX configurations.

Related Issue

N/A

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[ianstcdns]

@aggarg @RichardBarry

Submitting updated Xtensa port to FreeRTOS v11

I've created pull requests for Cadence's updated Xtensa FreeRTOS port and demo code. As you recommended, we have moved it to the Partner-Supported-Ports and Partner-Supported-Demos submodules, removed out-of-date code from the higher-level repos, and left a couple of READMEs in the old locations indicating the new home for this code.

Thank you in advance for your help reviewing this upstream request.

[aggarg]

Thank you for your contribution!