perf annotate: Sort by hottest lines in the TUI

Right now it will just sort and position at the hottest line, i.e.
the one where more samples were taken.

It will be at the center of the screen and later TAB/shift-TAB will
cycle thru the hottest lines.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>