Update BSP extension reference to avocado.target.board

[mobileoverlord]

Summary

Updates every reference example's avocado.yaml (and matching getting_started.md) to use avocado-bsp-{{ avocado.target.board }} instead of avocado-bsp-{{ avocado.target }}.

Why

Avocado 0.37 splits the target Jinja variable into a structured object with board (and carrier) sub-attributes. Previously avocado.target resolved to the board name as a flat string; going forward it's a dict, and the BSP extension name lives at avocado.target.board. This unblocks targets that pair a SoM/board with a separate carrier — the BSP extension is keyed on the board, while other parts of a manifest can reference the carrier independently.

Without this change, rendering a manifest under 0.37 produces avocado-bsp-{...} references that no longer resolve, and SDK/runtime resolution fails.

Scope

• 22 files changed, 46 substitutions (all reference projects under this repo).
• embedded-vision-summit/ is intentionally excluded (still untracked / WIP, not part of the standard reference set).

Test plan

• avocado build against a 0.37 SDK on at least one reference (e.g. qemu-quickstart) to confirm the templated extension name resolves.
• Spot-check a multi-target reference (e.g. react-dashboard, nodejs-dashboard, elixir-phoenix) where the BSP appears in multiple sections.