perf parse-events: Add default_breakpoint_len helper

perf parse-events: Add default_breakpoint_len helper

The default breakpoint length is "sizeof(long)" however this is
incorrect on platforms like Aarch64 where sizeof(long) is 8 but the
breakpoint length is 4. Add a helper function that can be used to
determine the correct breakpoint length, in this change it just
returns the existing default sizeof(long) value.

Use the helper in the bp_account test so that, when modifying the
event from a watchpoint to a breakpoint, the breakpoint length is
appropriate for the architecture and not just sizeof(long).

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Junhao He <hejunhao3@huawei.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yang Jihong <yangjihong@bytedance.com>
Link: https://lore.kernel.org/r/20240904050606.752788-5-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>