perf script: Enable to present DTL entries

perf script: Enable to present DTL entries

The process_event() function in "builtin-script.c" invokes
perf_sample__fprintf_synth() for displaying PERF_TYPE_SYNTH
type events.

   if (attr->type == PERF_TYPE_SYNTH && PRINT_FIELD(SYNTH))
   	perf_sample__fprintf_synth(sample, evsel, fp);

perf_sample__fprintf_synth() process the sample depending on the value
in evsel->core.attr.config. Introduce perf_sample__fprintf_synth_vpadtl()
and invoke this for PERF_SYNTH_POWERPC_VPA_DTL

Sample output:

   ./perf record -a -e sched:*,vpa_dtl/dtl_all/ -c 1000000000 sleep 1
   [ perf record: Woken up 1 times to write data ]
   [ perf record: Captured and wrote 0.300 MB perf.data ]

   ./perf script
            perf   13322 [002]   233.835807:                     sched:sched_switch: perf:13322 [120] R ==> migration/2:27 [0]
     migration/2      27 [002]   233.835811:               sched:sched_migrate_task: comm=perf pid=13322 prio=120 orig_cpu=2 dest_cpu=3
     migration/2      27 [002]   233.835818:               sched:sched_stat_runtime: comm=migration/2 pid=27 runtime=9214 [ns]
     migration/2      27 [002]   233.835819:                     sched:sched_switch: migration/2:27 [0] S ==> swapper/2:0 [120]
         swapper       0 [002]   233.835822:                                vpa-dtl: timebase: 338954486062657 dispatch_reason:decrementer_interrupt, preempt_reason:H_CEDE, enqueue_to_dispatch_time:435,			ready_to_enqueue_time:0, waiting_to_ready_time:34775058, processor_id: 202 c0000000000f8094 plpar_hcall_norets_notrace+0x18 ([kernel.kallsyms])
         swapper       0 [001]   233.835886:                                vpa-dtl: timebase: 338954486095398 dispatch_reason:priv_doorbell, preempt_reason:H_CEDE, enqueue_to_dispatch_time:542,			ready_to_enqueue_time:0, waiting_to_ready_time:1245360, processor_id: 201 c0000000000f8094 plpar_hcall_norets_notrace+0x18 ([kernel.kallsyms])

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Athira Rajeev <atrajeev@linux.ibm.com>
Tested-by: Tejas Manhas <tejas05@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: Aboorva Devarajan <aboorvad@linux.ibm.com>
Cc: Aditya Bodkhe <Aditya.Bodkhe1@ibm.com>
Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>