ttm_place are not supposed to change at runtime. All functions
working with ttm_place provided by <drm/ttm/ttm_placement.h> work
with const ttm_place. So mark the non-const structs as const.
File size before:
text data bss dec hex filename
2315 184 0 2499 9c3 drivers/gpu/drm/virtio/virtgpu_ttm.o
File size After adding 'const':
text data bss dec hex filename
2347 152 0 2499 9c3 drivers/gpu/drm/virtio/virtgpu_ttm.o