drm/xe: Annotate mcr_[un]lock()

drm/xe: Annotate mcr_[un]lock()

These functions acquire and release the gt::mcr_lock. Annotate
accordingly.
Fix the corresponding sparse warning.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Fixes: fb1d55efdfcb ("drm/xe: Cleanup OPEN_BRACE style issues")
Cc: Francois Dugast <francois.dugast@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240117134048.165425-4-thomas.hellstrom@linux.intel.com
(cherry picked from commit 97fd7a7e4e877676a2ab1a687ba958b70931abcc)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>