perf report/top: Add menu entry for toggling callchain expansion

Since previously pressing ENTER toggled expansion/collapse of callchain
entries and now brings up the same menu used when callchains are not
present, add an entry so that users can quickly figure out the change in
behaviour.

Its worth mentioning that we also always had 'e'/'c' to expand/collapse
all entries in a hist entry and 'E'/'C' for all hist entries.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-f9o03jo29fypvd8ly3j49d36@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>