drm/xe: Consolidate LRC offset calculations

drm/xe: Consolidate LRC offset calculations

Attempt to consolidate the LRC offsets calculations by aligning the
recently added wa_bb_offset with the naming scheme in the file and
also change the size stored in struct xe_lrc to not include the ring
buffer.

The former makes it somewhat visually easier to follow the layout of the
various logical blocks stored in the LRC bo, while the latter reduces the
number of sprinkled around calculations.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250630124711.8209-2-tvrtko.ursulin@igalia.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>