perf tools: Move event prototypes from util.h to event.h

perf tools: Move event prototypes from util.h to event.h

More needs to be done to have the actual functions and variables in a
smaller .c file that can then be included in the python binding,
avoiding dragging more stuff into it.

Link: http://lkml.kernel.org/n/tip-uecxz7cqkssouj7tlxrkqpl4@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>