drm/xe: Fix comments in xe_gt struct

drm/xe: Fix comments in xe_gt struct

Correct several spelling and grammar issues in xe_gt struct
documentation to improve readability:

- Fix "to not" -> "do not".
- Fix "mmigrations" -> "migrations".
- Fix "Multiple queues exists" -> "Multiple queues exist".
- Fix "are be processed" -> "to be processed".
- Fix "have being processed" -> "have been processed".

These changes are purely cosmetic and do not affect functionality.

v2: drop kernel-doc formatting change. (Jani)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20251006151317.2553182-2-shuicheng.lin@intel.com