perf trace: Fix segfault on perf trace -i perf.data

perf trace: Fix segfault on perf trace -i perf.data

When replaying a previous record session, it'll get a segfault since it
doesn't initialize raw_syscalls enter/exit tracepoint's evsel->priv for
caching the format fields.

So fix it by properly initializing sys_enter/exit evsels that comes from
reading the perf.data file header.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1384237500-22991-2-git-send-email-namhyung@kernel.org
[ Split the syscall tp field caching part in the previous patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>