perf tests: Add dwarf unwind test for powerpc

The user stack dump feature was recently added for powerpc. But there
was no test case available to test it.

This test works same as on other architectures by preparing a stack
frame on the perf test thread and comparing each frame by unwinding it.

  $ ./perf test 50
    50: Test dwarf unwind    : Ok

User stack dump for powerpc: https://lkml.org/lkml/2016/4/28/482

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1474267100-31079-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>