radv: Add wait-before-submit support for timelines.

radv: Add wait-before-submit support for timelines.

This is actually a non-threaded implementation. I'd summarize this
as event-based submission.

When submit happens we walk a tree of submissions that depend on
the syncobj signal operations to be submitted and if those submission
we no other dependencies we start to execute them immediately.

Or, well I still use a list to avoid issues with long chains and
the stacksize when using recursion.

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>