We don't have a 'perf test' entry available to test the watchpoint
functionality.

Add a simple set of tests:

 - Read only watchpoint
 - Write only watchpoint
 - Read / Write watchpoint
 - Runtime watchpoint modification

Ex.: on powerpc:

  $ sudo perf test 22
  22: Watchpoint                                            :
  22.1: Read Only Watchpoint                                : Ok
  22.2: Write Only Watchpoint                               : Ok
  22.3: Read / Write Watchpoint                             : Ok
  22.4: Modify Watchpoint                                   : Ok
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Kim Phillips <kim.phillips@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: http://lkml.kernel.org/r/20180912061229.22832-1-ravi.bangoria@linux.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>