drm/i915/bw: Rename struct intel_sa_info to intel_display_bw_params

drm/i915/bw: Rename struct intel_sa_info to intel_display_bw_params

To align with struct intel_platform_bw_params, rename struct
intel_sa_info to intel_display_bw_params.  Also add comments to contrast
their purposes.

v2:
  - Use gen11 and gen12 as prefixes for ICL's and TGL's display-specific
    parameters variables. (Matt)
  - Prefer to use "display" instead of "disp" in variable names. (Jani)
  - Drop the redundant "disp" from the variable names.

Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20260518-separate-platform-from-diplay-ip-specific-bw-params-v4-4-918528006549@intel.com
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>