drm/xe: Split xe_gt_stat.h

Follow what's done for the other headers, with the types split into a
separate header that can be included by other *_types.h headers.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241114152148.572447-5-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>