v3dv: create a v3dv_bo struct and reference it from v3dv_device_memory

So we have a lower level representation of a buffer object that we can
manipulate that is not tied to a Vulkan representation of memory. This
will be useful as we start allocating driver internal buffers, such as
command lists.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>
5 files changed