drm/ttm: move default BO destructor into VMWGFX v2

It's the only driver using this.

v2: use BUG_ON() in vmw_bo_create() as suggested by Zack

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220329110243.6335-5-christian.koenig@amd.com