tools: Move Makefile.arch from perf/config to tools/scripts

tools: Move Makefile.arch from perf/config to tools/scripts

After this patch other directories can use this architecture detector
without directly including it from perf's directory. Libbpf would
utilize it to get proper $(ARCH) so it can receive correct uapi include
directory.

Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1452520124-2073-8-git-send-email-wangnan0@huawei.com
[ Add missing srctree definition in tests/make ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@kernel.org>