perf evlist: Support pipe mode display

perf evlist: Support pipe mode display

Likewise, perf evlist command should print event attributes by reading
PERF_RECORD_HEADER_ATTR records.

Before:
  $ perf record -o- true | ./perf evlist -i-
  (prints nothing)

After:
  $ perf record -o- true | ./perf evlist -i-
  cycles:pppH

Committer testing:

Verbose mode also works as expected:

  $ perf record -o- true | perf evlist -i-
  cycles:uhH
  $ perf record -o- true | perf evlist -vi-
  cycles:uhH: size: 120, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|ID|PERIOD, read_format: ID, disabled: 1, inherit: 1, exclude_kernel: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
  $

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20201210061302.88213-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>