drm/xe: make xe_ttm_funcs const

Place the function pointers in rodata. Also drop the extra declaration
while at it.
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240117122044.1544174-1-jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/xe/xe_bo.c

@@ -1041,7 +1041,7 @@ static void xe_ttm_bo_delete_mem_notify(struct ttm_buffer_object *ttm_bo)
 	}
 }
 
-struct ttm_device_funcs xe_ttm_funcs = {
+const struct ttm_device_funcs xe_ttm_funcs = {
 	.ttm_tt_create = xe_ttm_tt_create,
 	.ttm_tt_populate = xe_ttm_tt_populate,
 	.ttm_tt_unpopulate = xe_ttm_tt_unpopulate,

drivers/gpu/drm/xe/xe_bo.h

@@ -243,7 +243,7 @@ int xe_bo_evict(struct xe_bo *bo, bool force_alloc);
 int xe_bo_evict_pinned(struct xe_bo *bo);
 int xe_bo_restore_pinned(struct xe_bo *bo);
 
-extern struct ttm_device_funcs xe_ttm_funcs;
+extern const struct ttm_device_funcs xe_ttm_funcs;
 
 int xe_gem_create_ioctl(struct drm_device *dev, void *data,
 			struct drm_file *file);

drivers/gpu/drm/xe/xe_vm.h

@@ -199,8 +199,6 @@ struct dma_fence *xe_vm_rebind(struct xe_vm *vm, bool rebind_worker);
 
 int xe_vm_invalidate_vma(struct xe_vma *vma);
 
-extern struct ttm_device_funcs xe_ttm_funcs;
-
 static inline void xe_vm_queue_rebind_worker(struct xe_vm *vm)
 {
 	xe_assert(vm->xe, xe_vm_in_preempt_fence_mode(vm));