perf bench: Rename 'mem-memcpy.c' => 'mem-functions.c'

So mem-memcpy.c started out as a simple memcpy() benchmark, then it grew
memset() functionality and now I plan to add string copy benchmarks as
well.

This makes the file name a misnomer: rename it to the more generic
mem-functions.c name.

Signed-off-by: Ingo Molnar <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Hitoshi Mitake <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
[ The "rename" was introducing __unused, wasn't removing the old file,
and didn't update tools/perf/bench/Build, fix it ]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/bench/Build

···
 perf-y += sched-messaging.o
 perf-y += sched-pipe.o
-perf-y += mem-memcpy.o
+perf-y += mem-functions.o
 perf-y += futex-hash.o
 perf-y += futex-wake.o
 perf-y += futex-wake-parallel.o