perf trace: Add flag/symbolic format_flags

It's useful to know whether a field is a flag or symbolic field
for e.g. when generating scripts - it allows us to translate
those fields specially rather than literally as plain numeric
values.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: fweisbec@gmail.com
Cc: rostedt@goodmis.org
Cc: anton@samba.org
Cc: hch@infradead.org
LKML-Reference: <1259133352-23685-3-git-send-email-tzanussi@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>