perf tools: callchain: Fix 'perf report' display to be callchain by default

perf tools: callchain: Fix 'perf report' display to be callchain by default

If we recorded with -g option to record the callchain, right now
we require a -g option to perf report as well - and people reported
this as unnecessary complication: the user already specified -g
once, no need to require it a second time.

So if the recording includes call-chains, display the callchain by
default from perf report.

( The user can override this default using "-g none" option from
  perf report. )

Reported-by: Ingo Molnar <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Mike Galbraith <[email protected]>
LKML-Reference: <1249690585[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>