Add support for platform root key

[sangho2]

This PR adds support for Platform Root Key (PRK) which can be used to derive other keys like per-TA keys. It introduces a new trait PlatformRootKeyProvider to let guests access PRK through the shim (platform_root_key()).

[sangho2]

@jaybosamiya-ms I've added PlatformRootKeyProvider to litebox, which is based on the discussion we had in the past.

[sangho2]

@tgopinath-microsoft This PR introduces a VTL function/call for setting a platform root key (mshv_vsm_set_platform_root_key). The function (and overall PR) is straightforward, but it requires your or your team's input because it defines a new ABI.

[sangho2]

Once this PR is merged, I'll rebase #643 .

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/enum_variant_added.ron

Failed in:
  variant VsmFunction:SetPlatformRootKey in /home/runner/work/litebox/litebox/litebox_platform_lvbs/src/mshv/mod.rs:158