CVE-2026-68247

In the Linux kernel, the following vulnerability has been resolved:

drm/i915/bios: range check LFP Data Block panel_type2

While the panel_type from LFP Data Block is range checked, panel_type2 is not. Add a few helpers for range checking, and use them to not only check panel_type2, but also improve clarity and correctness in the panel type selection.

Discovered using AI-assisted static analysis confirmed by Intel Product Security.

v2: - Fix commit message typo (Michał) - Add is_panel_type_pnp() (Ville)

(cherry picked from commit c9ebe5d2f25729d6cfbbb1235d640bf67f9275df)