modeset: honor forced FRL rate during link assessment

[Rohithmatham12]

Summary

• Treat nvidia-modeset.force_frl_rate as an explicit opt-in to use EDID-declared FRL capabilities during HDMI FRL link assessment.
• Leave the default physical link-training assessment path unchanged when force_frl_rate=0.
• Update the module parameter description so modinfo reflects the EDID-capability behavior.

This is intended to help forced/headless HDMI connectors where a valid override EDID advertises FRL (for example Max_FRL_Rate=6) but physical link assessment cannot complete because there is no real sink handshake, causing high-bandwidth modes such as 4K120 to be pruned.

Fixes #1184.

Testing

• git diff --check
• make -C kernel-open -n modules
  • Reached the kernel build handoff and then stopped in this macOS workspace because /lib/modules/25.5.0/build is not present.

I do not have the affected headless HDMI 2.1 setup locally, so this should be validated by the reporter or maintainers with nvidia-modeset.force_frl_rate=1 and/or nvidia-modeset.force_frl_rate=2.