Fix tier level for 5 thumb bare-metal ARM targets
The spec files for 5 Thumb-mode bare-metal ARM targets incorrectly set tier: Some(2), while the documentation correctly lists them as Tier 3. This mismatch was introduced in PR #150556 — the intent was Tier 2 eventually, but these targets should sit at Tier 3 until a proper Tier 3 → Tier 2 promotion MCP is submitted and approved.
This PR changes tier: Some(2) → Some(3) in the following spec files, making them consistent with the docs:
thumbv7a-none-eabi
thumbv7a-none-eabihf
thumbv7r-none-eabi
thumbv7r-none-eabihf
thumbv8r-none-eabihf
PS: No doc changes needed — they already correctly state Tier 3.
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Jonathan Brouwer
75234e5d66