perf tests: Disable breakpoint accounting test for powerpc

We disable this test as instruction breakpoints (HW_BREAKPOINT_X) are
not available for powerpc.

Before applying patch:

  21: Breakpoint accounting                                 :
  --- start ---
  test child forked, pid 3635
  failed opening event 0
  failed opening event 0
  watchpoints count 1, breakpoints count 0, has_ioctl 1, share 0
  test child finished with -2
  ---- end ----
  Breakpoint accounting: Skip

After applying patch:

  21: Breakpoint accounting                                 : Disabled
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20180412162140.2992-1-sandipan@linux.vnet.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/builtin-test.c

@@ -118,6 +118,7 @@ static struct test generic_tests[] = {
 	{
 		.desc = "Breakpoint accounting",
 		.func = test__bp_accounting,
+		.is_supported = test__bp_signal_is_supported,
 	},
 	{
 		.desc = "Number of exit events of a simple workload",