vmm/mmio: drop device registration names

The new API registers some devices without a numeric suffix. Multiple virtio input devices therefore share the same registration name, causing each registration to overwrite the previous device's boot metadata.

The names only serve as keys for collecting boot metadata; nothing looks devices up by name. Drop the names from the registration API and keep a record for each registered device so they all remain visible to the guest.

Assisted-by: OpenCode: GPT 6.1 Sol Assisted-by: Codex: GPT-6