perf report/top: Add 'k' hotkey to zoom directly into the kernel map

As a convenience, equivalent to pressing Enter in a line with a kernel
symbol and then selecting "Zoom" into the kernel DSO.

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-vbnlnrpyfvz9deqoobtc3dz7@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>