perf events parse: Rename parsing state struct to clearer name

perf events parse: Rename parsing state struct to clearer name

Rename it from 'parse_events_evlist' to 'parse_events_state' to better
state that this is parsing state that has to be passed around.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-dursqtg2h2w98ztaa297u43x@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>