radv/amdgpu: Use reference counting for bos.

radv/amdgpu: Use reference counting for bos.

Per the Vulkan spec, memory objects may be deleted before the buffers
and images using them are deleted, although those resources then
cannot be used except for deletion themselves.

For the virtual buffers, we need to access them on resource destruction
to unmap the regions, so this results in a use-after-free. Implement
reference counting to avoid this.

Signed-off-by: Bas Nieuwenhuizen <basni@google.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>