perf tools: Update some code references in design.txt

Update the names of some functions and enums in design.txt. The document
still has some stale information, but the motivation behind this patch
is to allow a developer to quickly grep and learn about the associated
structures.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1395169804-1293-1-git-send-email-artagnon@gmail.com


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