perf bench mem: Change 'cycle' to 'cycles'

So 'perf bench mem memset/memcpy' has a CPU cycles measurement method,
but calls it 'cycle' (singular) throughout the code, which makes it
harder to read.

Rename all related functions, variables and options to a plural 'cycles'
nomenclature.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1445241870-24854-8-git-send-email-mingo@kernel.org


[ s/--cycle/--cycles/g in perf-bench man page ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>