drm/xe: Document nested struct members according to guidelines

Document nested struct members with full names as described in
Documentation/doc-guide/kernel-doc.rst.

For this documentation we allow a column width of 100 to make
it more readable.

This fixes warnings similar to:
drivers/gpu/drm/xe/xe_lrc_types.h:45: warning: Excess struct member 'size' description in 'xe_lrc'

v2:
- Only change the documentation, not the member.

v3:
- Fix the commit message wording.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240123153147.27305-1-thomas.hellstrom@linux.intel.com