Claude review: drm/display: Add drm helper to check pr optimization support

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This adds a `pr_optimization_support` field to the tunnel struct, reads it from `DP_TUNNELING_CAPABILITIES` DPCD register at tunnel creation, and exposes a query function.

**Minor issue — typo in kdoc:**
```
 * Returns %true if the PR BW optimiation is supported for @tunnel.
```
"optimiation" → "optimization"

**Observation — no update on hotplug/re-detect:** The `pr_optimization_support` flag is only set in `create_tunnel()`. Looking at `tunnel_info_changes_are_valid()`, changes to `bw_alloc_supported` are detected and flagged, but there's no equivalent check for `pr_optimization_support`. This is probably fine in practice since the tunneling capabilities register is unlikely to change at runtime without a full disconnect/reconnect (which would destroy and recreate the tunnel), but it's worth noting for consistency. Not a blocker.

**The stub for `CONFIG_DRM_DISPLAY_DP_TUNNEL=n` is correct** — returns false.

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