Add support for setting up platform root key for LVBS

[sangho2]

This PR adds support for setting up the Platform Root Key for the LVBS platform, which can be used to derive other keys like per-TA keys.

[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 .

[jaybosamiya-ms]

Thanks @sangho2! For visibility, Sangho and I discussed this PR offline, and I've instead introduced #781 as the alternate interface to consider, which balances both the OP-TEE requirements as well as more distrustful platforms.

[tgopinath-microsoft]

Do you think we will have the key size to be something other than 8 bytes ? If no, may be just need the key_pa and we do not need the size argument ? If you think we should extend the root key to be more than 8 bytes, then maybe we can have a an array of 8 bytes for key_pa and then specify the size in key_size

[sangho2]

I think the key should be at least 32 bytes (16 bytes might be okay but a bit weak)? If this something about we don't need to support various key size options, I think it is okay to only support a 32-byte root key.

[tgopinath-microsoft]

Ah I somehow mistook key_pa as key. ok then let us just support a 32 byte key and do away with the size

[sangho2]

sounds good. I'll revise the function signature.

[sangho2]

revised.

[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