perf streams: Calculate the sum of total streams hits

perf streams: Calculate the sum of total streams hits

We have used callchain_node->hit to measure the hot level of one stream.
This patch calculates the sum of hits of total streams.

Thus in next patch, we can use following formula to report hot percent
for one stream.

hot percent = callchain_node->hit / sum of total hits

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20201009022845.13141-6-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>