drm/ttm: let struct ttm_device_funcs be placed in rodata

Make the struct ttm_device_funcs pointers const so the data can be placed in rodata.

Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230309123700.528641-1-jani.nikula@intel.com

drivers/gpu/drm/ttm/ttm_device.c

@@ -189,7 +189,7 @@ EXPORT_SYMBOL(ttm_device_swapout);
  * Returns:
  * !0: Failure.
  */
-int ttm_device_init(struct ttm_device *bdev, struct ttm_device_funcs *funcs,
+int ttm_device_init(struct ttm_device *bdev, const struct ttm_device_funcs *funcs,
 		    struct device *dev, struct address_space *mapping,
 		    struct drm_vma_offset_manager *vma_manager,
 		    bool use_dma_alloc, bool use_dma32)

include/drm/ttm/ttm_device.h

@@ -223,7 +223,7 @@ struct ttm_device {
 	 * @funcs: Function table for the device.
 	 * Constant after bo device init
 	 */
-	struct ttm_device_funcs *funcs;
+	const struct ttm_device_funcs *funcs;
 
 	/**
 	 * @sysman: Resource manager for the system domain.
@@ -287,7 +287,7 @@ static inline void ttm_set_driver_manager(struct ttm_device *bdev, int type,
 	bdev->man_drv[type] = manager;
 }
 
-int ttm_device_init(struct ttm_device *bdev, struct ttm_device_funcs *funcs,
+int ttm_device_init(struct ttm_device *bdev, const struct ttm_device_funcs *funcs,
 		    struct device *dev, struct address_space *mapping,
 		    struct drm_vma_offset_manager *vma_manager,
 		    bool use_dma_alloc, bool use_dma32);