perf hists browser: Allow passing an initial hotkey

Sometimes we're in an outer code, like the main hists browser popup menu
and the user follows a suggestion about using some hotkey, and that
hotkey is really handled by hists_browser__run(), so allow for calling
it with that hotkey, making it handle it instead of waiting for the user
to press one.

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-xv2l7i6o4urn37nv1h40ryfs@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>