perf tools: Add new mem command for memory access profiling

This new command is a wrapper on top of perf record and perf report to
make it easier to configure for memory access profiling.

To record loads:
$ perf mem -t load rec .....

To record stores:
$ perf mem -t store rec .....

To get the report:
$ perf mem -t load rep

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1359040242-8269-15-git-send-email-eranian@google.com
[ Fixed minor conflict with 66857b5 "Sort command-list.txt alphabetically" ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>