perf scripts: Fallback to syscalls:* when raw_syscalls:* is not available

perf scripts: Fallback to syscalls:* when raw_syscalls:* is not available

Older kernels (e.g., RHEL6) do system call tracing via the
syscalls:sys_{enter,exit} tracepoints rather than using raw_syscalls:*.

Update perf python and perl scripts to fallback to syscalls:* when
raw_syscalls:* isn't available.

Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/5a6c64081a3375bc3bc66351b14559678ef4d71e.1402507908.git.bristot@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>