perf annotate: Show full source location with 'l' hotkey

Right now, when Line numbers are displayed, one can't easily find a
source file that the line corresponds to.

When a source line is selected and 'l' is pressed, full source file
location is displayed in perf UI footer line. The hotkey works only for
source code lines.

Signed-off-by: Martin Liška <mliska@suse.cz>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lore.kernel.org/lkml/25a6384f-d862-5dda-4fec-8f0555599c75@suse.cz


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