powerpc/selftests: Add selftest to test concurrent perf/ptrace events

ptrace and perf watchpoints can't co-exists if their address range
overlaps. See commit 29da4f91

 ("powerpc/watchpoint: Don't allow
concurrent perf and ptrace events") for more detail. Add selftest
for the same.

Sample o/p:
  # ./ptrace-perf-hwbreak
  test: ptrace-perf-hwbreak
  tags: git_version:powerpc-5.8-7-118-g937fa174a15d-dirty
  perf cpu event -> ptrace thread event (Overlapping): Ok
  perf cpu event -> ptrace thread event (Non-overlapping): Ok
  perf thread event -> ptrace same thread event (Overlapping): Ok
  perf thread event -> ptrace same thread event (Non-overlapping): Ok
  perf thread event -> ptrace other thread event: Ok
  ptrace thread event -> perf kernel event: Ok
  ptrace thread event -> perf same thread event (Overlapping): Ok
  ptrace thread event -> perf same thread event (Non-overlapping): Ok
  ptrace thread event -> perf other thread event: Ok
  ptrace thread event -> perf cpu event (Overlapping): Ok
  ptrace thread event -> perf cpu event (Non-overlapping): Ok
  ptrace thread event -> perf same thread & cpu event (Overlapping): Ok
  ptrace thread event -> perf same thread & cpu event (Non-overlapping): Ok
  ptrace thread event -> perf other thread & cpu event: Ok
  success: ptrace-perf-hwbreak

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210412112218.128183-5-ravi.bangoria@linux.ibm.com