perf tools: Improve libperl detection message

Before:

  Missing perl devel files. Disabling perl scripting support, consider installing perl-ExtUtils-Embed

After:

  Missing perl devel files. Disabling perl scripting support, please install perl-ExtUtils-Embed/libperl-dev

Change the message to the standard 'please install' language and
adds Debian-ish package suggestion.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <david.ahern@oracle.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150228083909.GC31887@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>