MIPS: Loongson: Add support for perf tool

In order to use perf tool on the Loongson platform, we should enable kernel
support for various performance events provided by software and hardware,
so add CONFIG_PERF_EVENTS=y to loongson3_defconfig.

E.g. without this patch:

[loongson@localhost perf]$ ./perf list

List of pre-defined events (to be used in -e):

  duration_time                                      [Tool event]

  rNNN                                               [Raw hardware event descriptor]
  cpu/t1=v1[,t2=v2,t3 ...]/modifier                  [Raw hardware event descriptor]
   (see 'man perf-list' on how to encode it)

  mem:<addr>[/len][:access]                          [Hardware breakpoint]

With this patch:

[loongson@localhost perf]$ ./perf list

List of pre-defined events (to be used in -e):

  branch-instructions OR branches                    [Hardware event]
  branch-misses                                      [Hardware event]
  cpu-cycles OR cycles                               [Hardware event]
  instructions                                       [Hardware event]

  alignment-faults                                   [Software event]
  bpf-output                                         [Software event]
  context-switches OR cs                             [Software event]
  cpu-clock                                          [Software event]
  cpu-migrations OR migrations                       [Software event]
  dummy                                              [Software event]
  emulation-faults                                   [Software event]
  major-faults                                       [Software event]
  minor-faults                                       [Software event]
  page-faults OR faults                              [Software event]
  task-clock                                         [Software event]

  duration_time                                      [Tool event]

  L1-dcache-load-misses                              [Hardware cache event]
  L1-dcache-store-misses                             [Hardware cache event]
  L1-icache-load-misses                              [Hardware cache event]
  branch-load-misses                                 [Hardware cache event]
  branch-loads                                       [Hardware cache event]
  dTLB-load-misses                                   [Hardware cache event]
  dTLB-store-misses                                  [Hardware cache event]
  iTLB-load-misses                                   [Hardware cache event]

  rNNN                                               [Raw hardware event descriptor]
  cpu/t1=v1[,t2=v2,t3 ...]/modifier                  [Raw hardware event descriptor]
   (see 'man perf-list' on how to encode it)

  mem:<addr>[/len][:access]                          [Hardware breakpoint]
Signed-off-by: NTiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: NThomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/configs/loongson3_defconfig

@@ -21,6 +21,7 @@ CONFIG_SYSFS_DEPRECATED=y
 CONFIG_RELAY=y
 CONFIG_BLK_DEV_INITRD=y
 CONFIG_EMBEDDED=y
+CONFIG_PERF_EVENTS=y
 CONFIG_MACH_LOONGSON64=y
 CONFIG_SMP=y
 CONFIG_HZ_256=y