perf script: Extend misc field decoding with switch out event type

Append 'p' sign to 'S' tag designating the type of context switch out event so
'Sp' means preemption context switch. Documentation is extended to cover
new presentation changes.

  $ perf script --show-switch-events -F +misc -I -i perf.data:

          hdparm 4073 [004] U  762.198265:     380194 cycles:ppp:      7faf727f5a23 strchr (/usr/lib64/ld-2.26.so)
          hdparm 4073 [004] K  762.198366:     441572 cycles:ppp:  ffffffffb9218435 alloc_set_pte (/lib/modules/4.16.0-rc6+/build/vmlinux)
          hdparm 4073 [004] S  762.198391: PERF_RECORD_SWITCH_CPU_WIDE OUT          next pid/tid:    0/0
         swapper    0 [004]    762.198392: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid: 4073/4073
         swapper    0 [004] Sp 762.198477: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt  next pid/tid: 4073/4073
          hdparm 4073 [004]    762.198478: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid:    0/0
         swapper    0 [007] K  762.198514:    2303073 cycles:ppp:  ffffffffb98b0c66 intel_idle (/lib/modules/4.16.0-rc6+/build/vmlinux)
         swapper    0 [007] Sp 762.198561: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt  next pid/tid: 1134/1134
  kworker/u16:18 1134 [007]    762.198562: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid:    0/0
  kworker/u16:18 1134 [007] S  762.198567: PERF_RECORD_SWITCH_CPU_WIDE OUT          next pid/tid:    0/0

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5fc65ce7-8ca5-53ae-8858-8ddd27290575@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>