perf ui browser: Optional horizontal scrolling key binding

If the classes derived from ui_browser want to do some sort of
horizontal scrolling, they have just to set ui_browser->columns to
the number of columns available.

Those columns can be the number of characters on the screen, if what is
desired is to scroll character by character, or the number of columns in
a spreadsheet like table.

This is what the hist_browser will do, skipping ui_browser->horiz_scroll
columns when rendering each of its lines.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-q6a22bpmpgcr1awgzrmd4jrs@git.kernel.org


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