perf hists browser: Save perf_session_env in the hist_browser

The perf_session_env is to save system informantion at the recording
time to be refered in the hist browser.  So it'd be better to keep in
the struct hist_browser.  This is a preparation to later change.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1429687101-4360-7-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>