Add a feature flag for firmware for 2.1 HW.

[swenson]

This is an additive flag to turn on 2.1 features, particularly for ROM (I3C AXI recovery bypass) and eventually for SPDM (ML-KEM, external mu support for ML-DSA).

This adds support for switching versions when using cargo xtask runtime, which will ensure that the firmware is built with the hw-2-1 flag if running the emulator for 2.1.

[Copilot]

Pull Request Overview

This PR introduces a --hw-revision flag to the cargo xtask runtime command and a corresponding hw-2-1 feature flag for firmware crates, enabling 2.1 hardware features (I3C AXI recovery bypass, ML-KEM support).

• Add hw_revision argument in xtask/src/main.rs and handle it in xtask/src/runtime.rs to automatically include the hw-2-1 flag when building.
• Update Cargo.toml for multiple crates to define and expose the new hw-2-1 feature.
• Wrap ROM flash recovery flow in a cfg!(feature = "hw-2-1") guard and document hardware revision usage in README.md.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
xtask/src/main.rs	Added --hw-revision CLI flag with default 2.0.0.
xtask/src/runtime.rs	Inject hw-2-1 feature into build flags when needed.
rom/src/rom.rs	Guard flash recovery code with hw-2-1 feature.
rom/Cargo.toml	Define hw-2-1 feature for ROM crate.
platforms/emulator/runtime/userspace/apps	Add hw-2-1 feature to user and example app crates.
platforms/emulator/runtime/Cargo.toml	Define hw-2-1 feature for emulator runtime crate.
platforms/emulator/rom/Cargo.toml	Define hw-2-1 and attach it to common code.
README.md	Document hardware revision workflow and flags.

Comments suppressed due to low confidence (2)

xtask/src/runtime.rs:33

• Add unit tests around this branch to verify that the hw-2-1 flag is only pushed into the features list when hw_revision >= 2.1.0, and not otherwise.

    if hw_revision >= semver::Version::new(2, 1, 0) {

README.md:50

• [nitpick] Include a brief example showing how to enable hw-2-1 in Cargo.toml or via cargo build --features hw-2-1 to make it clearer for users.

For firmware, 2.1 features can be enabled using the `hw-2-1` feature flag when specifying dependencies.

[helloxiling]

Looks good to me.

[swenson]

Thanks!