perf bench mem: Move boilerplate memory allocation to the infrastructure

Instead of having all tests perform alloc/free, do it in the code that
calls the do_cycles() and do_gettimeofday() functions.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
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-lywj4mbdb1m9x1z9asivwuuy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>