perf tests: Aename open*.c to openat*.c

Since the test being tested is now openat rather than open, rename the
files to make it explicit. The patch is separeted from the first to make
it simpler to deal with any potential conflicts in the Makefile
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>
Reviewed-by: NIngo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1429192375-13706-3-git-send-email-riku.voipio@linaro.org
[ Fixed it up wrt Build files ]
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/Build

@@ -3,9 +3,9 @@ perf-y += parse-events.o
 perf-y += dso-data.o
 perf-y += attr.o
 perf-y += vmlinux-kallsyms.o
-perf-y += open-syscall.o
-perf-y += open-syscall-all-cpus.o
-perf-y += open-syscall-tp-fields.o
+perf-y += openat-syscall.o
+perf-y += openat-syscall-all-cpus.o
+perf-y += openat-syscall-tp-fields.o
 perf-y += mmap-basic.o
 perf-y += perf-record.o
 perf-y += rdpmc.o