perf script: Separate events from branch types

perf script: Separate events from branch types

Branch types and events are two different things.  A branch type can be
a conditional branch, an indirect branch, a procedure call, a return, or
an exception taken, etc.  The extra event information is provided for
what happens during a branch, e.g. if a branch is mispredicted or not
taken (specific to conditional branches).

To deliver information about branches, this commit separates events from
branch types.  It parses branch types first, then appends event strings
embraced by the '/' character.  If multiple events occur, the events is
separated with a comma (,).

Also add a minor improvement by adding char 'm' in char array for branch
mispredict event.

Below are extracted sample flags.

Before:
        branch:   br miss
  instructions:   br miss

After:
        branch:   jmp/miss/
  instructions:   jmp/miss/

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/r/20250304111240.3378214-4-leo.yan@arm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>