drm/vmwgfx: Fix the lifetime of the bo cursor memory

In the Linux kernel, the following vulnerability has been resolved: drm/vmwgfx: Fix the lifetime of the bo cursor memory The cleanup can be dispatched while the atomic update is still active, which means that the memory acquired in the atomic update needs to not be invalidated by the cleanup. The buffer objects in vmw_plane_state instead of using the builtin map_and_cache were trying to handle the lifetime of the mapped memory themselves, leading to crashes. Use the map_and_cache instead of trying to manage the lifetime of the buffer objects held by the vmw_plane_state. Fixes kernel oops'es in IGT's kms_cursor_legacy forked-bo.