drm/i915/display: Add link rate and lane count to i915_display_info

drm/i915/display: Add link rate and lane count to i915_display_info

Adding link rate and lane count information to i915_display_info makes it
easier and faster to access this data compared to checking kernel logs.
This is particularly beneficial for individuals who are not familiar with
i915 in the following scenarios:

* Debugging DP tunnel bandwidth usage in the Thunderbolt driver.
* During USB4 certification, it is necessary to know the link rate used by
  the monitor to prove that the DP tunnel can handle required rates.
* In PHY CTS, when the connector probes are not mounted correctly,
  some display lanes may not appear in the DP Oscilloscope, leading to CTS
  failures.

This change provides validation teams with an easy way to identify and
troubleshoot issues.

v2: separate seq_printf line (Jani)
v3: separate output line (Jani)

Cc: Imre Deak <imre.deak@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20250409230214.963999-1-khaled.almahallawy@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>