freertos-mpu: Add Privileged eXecute Never MPU attribute support

[AhmedIsmail02]

A new MPU region attribute Privileged eXecute Never (PXN) is introduced in Armv8.1-M architecture, where if an MPU region has PXN attribute set and the processor attempts to execute the code inside with privileged level, the Memory Management Fault exception would be triggered, with IACCVIOL bit in MemManage Fault State Register set to 1. The PXN feature allows privileged software to ensure specific application tasks (threads) to execute in unprivileged level only.

This PR adds the new MPU region attribute Privileged eXecute Never (PXN) support to the Armv8.1-M architecture port variants.

Description

Test Steps

Checklist:

• [x] I have tested my changes. No regression in existing tests.
• [ ] I have modified and/or added unit-tests to cover the code changes in this Pull Request.

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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[AhmedIsmail02]

Hi @aggarg, Just checking if i should squash the code review suggestions commit with the existing commit ?

[aggarg]

@AhmedIsmail02, Yes, I have squashed and merged. Thank you for your contribution!