perf annotate: Add PERCENT_PERIOD_GLOBAL percent value

perf annotate: Add PERCENT_PERIOD_GLOBAL percent value

Adding and computing global period percent value for annotation line.
Storing it in struct annotation_data percent array under new
PERCENT_PERIOD_GLOBAL index.

At the moment it's not displayed, it's coming in following patches.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20180804130521.11408-12-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>