drm/ttm: Use a struct for the common part of struct ttm_lru_walk and struct ttm_bo_lr...

drm/ttm: Use a struct for the common part of struct ttm_lru_walk and struct ttm_bo_lru_cursor

Let the locking functions take the new struct ttm_lru_walk_arg
as argument in order for them to be easily used from both
types of walk.

v2:
- Whitespace fix

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250623155313.4901-2-thomas.hellstrom@linux.intel.com