perf tools: Add test for building detached source tarballs

perf tools: Add test for building detached source tarballs

Test one of the main kernel Makefile targets to generate a perf sources
tarball suitable for build outside the full kernel sources.

This is to test that the tools/perf/MANIFEST file lists all the files
needed to be in such tarball, which sometimes gets broken when we move
files around, like when we made some files that were in tools/perf/
available to other tools/ codebases by moving it to tools/include/, etc.

Now everytime we use 'make -C tools/perf -f tests/make' this test will
be performed, helping detect such problems earlier in the devel cycle.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-gyivwbbu2j7c4j4pwpmttg2p@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>