export pmu data from perf_event_open.c

export the perf_event_open() pmus structure, that way perf_fuzzer can
pretty-print the pmu names.  It saves a lot of code duplication.

I could always just make this change in my local tree, but it's nice
having perf_event_open.c the same in both projects.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>