drm/ttm/vmwgfx: move ttm_bo_wait into VMWGFX

Not used anymore by other drivers or TTM itself.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221125102137.1801-9-christian.koenig@amd.com