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