perf tools: Rename build libperf to perf

Rename build libperf to perf, because it's used to build perf.

The libperf build object name will be used for libperf library.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190213123246.4015-4-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/arch/xtensa/Build b/tools/perf/arch/xtensa/Build
index 54afe4a..e4e5f33 100644
--- a/tools/perf/arch/xtensa/Build
+++ b/tools/perf/arch/xtensa/Build
@@ -1 +1 @@
-libperf-y += util/
+perf-y += util/