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

[dymk]

Summary

Adds a Battery FFA service to the QEMU SBSA secure partition, backed by a real EC connection over PL011 UART using MCTP serial (DSP0253) framing.

New crates

• sp-mctp-framer — Lightweight MCTP serial framing layer on top of mctp-rs. Handles DSP0253 byte-stuffing, CRC-16, and packet assembly/disassembly over a raw byte stream.
• qemu-sp-uart — Minimal PL011 MMIO UART driver for the secure partition (polled mode, no interrupts).

Changes to existing crates

• qemu-sp — Wires up the new Battery FFA handler + EC relay pipeline: FFA request → MCTP serialize → PL011 TX → PL011 RX → MCTP deserialize → FFA response.

Architecture

UEFI (NS) ──FFA──▶ SP (qemu-sp)
                      │
                      ├── BatteryFfaHandler
                      │     └── ec_relay::send_request()
                      │           ├── sp-mctp-framer::serialize
                      │           ├── qemu-sp-uart::write
                      │           ├── qemu-sp-uart::read
                      │           └── sp-mctp-framer::deserialize
                      │
                      └── PL011 UART ──serial──▶ EC (dev-qemu)

[Copilot]

Pull request overview

Adds initial building blocks for a QEMU SBSA secure-partition EC relay path by introducing a minimal PL011 UART driver crate and adding MCTP-based relay + Battery service plumbing in ec-service-lib, along with dependency/supply-chain updates.

Changes:

• Added new qemu-sp-uart crate providing a blocking, polled PL011 MMIO UART driver with host-side unit tests.
• Added ec-service-lib EC relay infrastructure (ec_relay) and a Battery service that proxies GetBst over MCTP serial framing.
• Updated workspace dependencies (mctp-rs, embedded-services crates), lockfiles, cargo-vet config/imports, and cargo-deny advisories ignore list.

Reviewed changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
supply-chain/imports.lock	Updates imported cargo-vet audit entries to cover new/transitive dependencies.
supply-chain/config.toml	Updates cargo-vet exemptions for updated dependency graph.
qemu-sp-uart/src/lib.rs	New no_std PL011 UART driver with an MMIO abstraction and host tests.
qemu-sp-uart/README.md	Crate documentation describing API/usage and safety contract.
qemu-sp-uart/Cargo.toml	Adds the new UART crate to the workspace with no external deps.
ec-service-lib/src/services/mod.rs	Registers new battery and ec_relay service modules and exports.
ec-service-lib/src/services/ec_relay.rs	Introduces transport-agnostic ODP-over-MCTP relay and a UART-based serial transport.
ec-service-lib/src/services/battery.rs	Adds Battery proxy service using the relay and a host-only wire-format compatibility test.
ec-service-lib/Cargo.toml	Adds dependencies for MCTP serial + UART crate and host-only test deps for wire-format gating.
deny.toml	Ignores RUSTSEC-2024-0436 for paste (transitive via embedded-services).
Cargo.toml	Adds qemu-sp-uart workspace member and new git-based workspace dependencies.
Cargo.lock	Updates dependency resolution to include embedded-services/mctp-rs and related crate version bumps.

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[dymk]

Recreating from fork branch to allow force-push updates.