feat: add Battery FFA service + MCTP-via-PL011 EC relay

[dymk]

Summary

Adds Battery FFA service infrastructure and MCTP-via-PL011 EC relay to ec-service-lib, plus a minimal PL011 MMIO UART driver crate. The wiring into qemu-ec-sp's message loop (replacing the existing stub Battery handler) is done in the platform integration PR that updates the submodule pointer.

New crates

• qemu-sp-uart — Minimal PL011 MMIO UART driver for the secure partition (polled mode, no interrupts).

Changes to existing crates

• ec-service-lib — New ec_relay module: generic ODP-over-MCTP relay infrastructure with MctpSerialTransport. New battery service module backed by the relay. QEMU PL011 UART support is gated behind the qemu-pl011 feature for clean layering.

Architecture

UEFI (NS) ──FFA──▶ SP (qemu-sp)
                      │
                      ├── BatteryFfaHandler
                      │     └── ec_relay::invoke()
                      │           ├── MCTP serialize (mctp-rs)
                      │           ├── DSP0253 serial framing
                      │           ├── PL011 UART TX/RX
                      │           └── MCTP deserialize
                      │
                      └── PL011 UART ──serial──▶ EC (dev-qemu)

Scope note

This PR delivers the library-side implementation. The platform wiring (replacing qemu-sp's stub Battery with the relay-backed version) happens in the odp-platform-qemu-sbsa integration PR that updates the mod/secure-services submodule pointer.

[Copilot]

Pull request overview

This PR introduces SP-side infrastructure to proxy FFA service requests to an external EC over MCTP serial framing carried on a PL011 UART (QEMU SBSA secure partition use-case), and adds an initial Battery service built on that relay. It also wires in new workspace members/dependencies and updates cargo-vet/cargo-deny configuration accordingly.

Changes:

• Add new qemu-sp-uart crate providing a minimal no_std, polled PL011 MMIO UART driver (with host-side unit tests via a mock MMIO backend).
• Add ec-service-lib::services::ec_relay (ODP-over-MCTP relay + UART transport abstraction) and ec-service-lib::services::battery (GetBst proxy service using the relay).
• Update workspace/dependency lockfiles and supply-chain policy (cargo-vet imports/exemptions, cargo-deny advisory ignore).

Reviewed changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
supply-chain/imports.lock	Updates cargo-vet import lock to include newly introduced dependency audit entries.
supply-chain/config.toml	Updates cargo-vet exemptions for new/updated dependencies (incl. MCTP/serial transitive deps).
qemu-sp-uart/src/lib.rs	Implements the PL011 MMIO UART driver plus mock-based unit tests.
qemu-sp-uart/README.md	Documents the UART crate’s scope, API, base-address contract, and safety requirements.
qemu-sp-uart/Cargo.toml	Declares the new workspace crate metadata and lint configuration.
ec-service-lib/src/services/mod.rs	Registers/exports the new Battery service and relay types.
ec-service-lib/src/services/ec_relay.rs	Adds the ODP-over-MCTP relay, transport traits, and MCTP serial transport implementation.
ec-service-lib/src/services/battery.rs	Adds Battery FFA service implementation using the relay, plus a host wire-format gate test.
ec-service-lib/Cargo.toml	Adds mctp-rs dependency, optional qemu-sp-uart, and host-only dev-deps for wire-format tests.
deny.toml	Adds a cargo-deny advisory ignore for paste (transitive).
Cargo.toml	Adds qemu-sp-uart workspace member and new git-sourced workspace dependencies (mctp-rs, embedded-services crates).
Cargo.lock	Updates lockfile for new crates and dependency version bumps introduced by the relay stack.

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[philgweber]

We should add a read_byte with timeout and primarily use that as SP is usually on a single CPU and no scheduler. We ran into forever loops if EC was not attached and responding on the O6 demo. This is fine to get the service up and running, but will need to add error handling and recovery at some point.

[kurtjd]

Have you considered using the existing embedded-io trait: https://docs.rs/embedded-io/latest/embedded_io/
This is typically implemented by many HALs for uart drivers (and is, for example, what the uart-service on the EC side is generic over).