drm/i915/xe3p_lpd: Handle underrun debug bits

drm/i915/xe3p_lpd: Handle underrun debug bits

Xe3p_LPD added several bits containing information that can be relevant
to debugging FIFO underruns.  Add the logic necessary to handle them
when reporting underruns.

This was adapted from the initial patch[1] from Sai Teja Pottumuttu.

[1] https://lore.kernel.org/all/20251015-xe3p_lpd-basic-enabling-v1-12-d2d1e26520aa@intel.com/

v2:
  - Handle FBC-related bits in intel_fbc.c. (Ville)
  - Do not use intel_fbc_id_for_pipe (promoted from
    skl_fbc_id_for_pipe), but use pipe's primary plane to get the FBC
    instance. (Ville, Matt)
  - Improve code readability by moving logic specific to logging fields
    of UNDERRUN_DBG1 to a separate function. (Jani)

v3:
  - Use crtc->base.primary instead of cycling through all crtcs

Bspec: 69111, 69561, 74411, 74412
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patch.msgid.link/20251202012306.9315-5-matthew.s.atwood@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>