libgscaler: Add support for sync

Changed gsc_out_run to return the fence returned by qbuf and to
dequeue a buffer only when all buffers have been enqueued.
Start streaming after one buffer has been enqueued.

Bug: 7123196
Change-Id: Ib2a563b9d39888d66f0d4a37c79fde2f7b7140fa
3 files changed