Handling of the startup issues related to the CPU features

[esmakokten]

Summary of this Pull Request (PR)

• Disabled MPK (using MPK_ENABLED compile switch) on the main branch.
• Added a check for PCID support to generate more meaningful error.

Choose one (Mandatory):

• [ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• [x] This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory): @gparmer @WenyuanShao

Code Quality

As part of this pull request, I've considered the following:

Style:

• [x] Comments adhere to the Style Guide (SG)
• [x] Spacing adhere's to the SG
• [ ] Naming adhere's to the SG
• [ ] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
• [x] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

Code Craftsmanship:

• [ ] I've made an attempt to remove all redundant code
• [x] I've considered ways in which my changes might impact existing code, and cleaned it up
• [ ] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [x] I've commented appropriately where code is tricky
• [x] I agree that there is no "throw-away" code, and that code in this PR is of high quality

Testing

I've tested the code using the following test programs (provide list here):

• [ ] micro_booter (corresponding toml file?)
• [x] unit_pingpong (with sched_pingpong.toml PASSED, ping_pong.toml fails on main)
• [x] unit_schedtests (with sched.toml)
• [x] pingpong with/wo MPK_ENABLED, with/wo CPU pcid support.

Testing environment is my laptop using qemu.