perf report/top: Allow pressing hotkeys in the options popup menu

When the users presses ENTER in the main 'perf report/top' screen a
popup menu is presented, in it some hotkeys are suggested as
alternatives to using the menu, or for additional features.

At that point the user may try those hotkeys, so allow for that by
recording the key used and exiting, the caller then can check for that
possibility and process the hotkey.

I.e. try pressing ENTER, and then 'k' to exit and zoom into the kernel
map, using ESC then zooms out, etc.

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: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-ujfq3fw44kf6qrtfajl5dcsp@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>