goldfish-opengl: one virtgpu instance per HostConnection

When in virtio mode -- even with ASG -- gfxstream opens an ancillary
rendernode fd to perform the process pipe logic.  Reuse the already
existing one from the stream.

BUG=202552093
TEST=compile

Change-Id: I32d2f42afa744ca681aff815d00b3e85158c347b
8 files changed