tmf/lttng2: support multiple symbol providers

tmf/lttng2: support multiple symbol providers

The basic symbol provider is now available for all call stack
analyses.

Change-Id: Ic359d12b4027977ca4a2e6c3cb30e1c780c92e41
Signed-off-by: Mikael Ferland <mikael.ferland@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/97924
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Reviewed-by: Hudson CI