perf session: Print branch stack entry type in --dump-raw-trace

This can help with debugging issues. It only prints when -j save_type
is used otherwise an empty string is printed.

Before the change:

  101603801707130 0xa70 [0x630]: PERF_RECORD_SAMPLE(IP, 0x2): 1108/1108: 0xffff9c1df24c period: 10694 addr: 0
  ... branch stack: nr:64
  .....  0: 0000ffff9c26029c -> 0000ffff9c26f340 0 cycles  P   0
  .....  1: 0000ffff9c2601bc -> 0000ffff9c26f340 0 cycles  P   0

After the change:

  101603801707130 0xa70 [0x630]: PERF_RECORD_SAMPLE(IP, 0x2): 1108/1108: 0xffff9c1df24c period: 10694 addr: 0
  ... branch stack: nr:64
  .....  0: 0000ffff9c26029c -> 0000ffff9c26f340 0 cycles  P   0 CALL
  .....  1: 0000ffff9c2601bc -> 0000ffff9c26f340 0 cycles  P   0 IND_CALL

Signed-off-by: James Clark <james.clark@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220307171917.2555829-3-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>