perf ui/tui: Add 'F' hotkey to toggle percentage output

Add 'F' hotkey to toggle relative and absolute percentage of filtered
entries.

Suggested-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
perf tools: Show absolute percentage by default

Now perf report will show absolute percentage on filter entries by
default.

Suggested-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>