rta: add live_callsites and live_callsites

In a callgraph it is useful to be able to compute the live target of any
callsite

Signed-off-by: Jean Privat <jean@pryen.org>
metrics/rta: add callsite_info to display things

Signed-off-by: Jean Privat <jean@pryen.org>
tests: update sav/nitmetrics_args1.res for RTA-callsite info

Signed-off-by: Jean Privat <jean@pryen.org>