perf evsel: Add accessor for tool_event

perf evsel: Add accessor for tool_event

Currently tool events use a dedicated variable within the evsel. Later
changes will move this to the unused struct perf_event_attr config for
these events. Add an accessor to allow the later change to be well
typed and avoid changing all uses.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20240907050830.6752-4-irogers@google.com
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Yang Jihong <yangjihong@bytedance.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: Clément Le Goffic <clement.legoffic@foss.st.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ze Gao <zegao2021@gmail.com>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Cc: Changbin Du <changbin.du@huawei.com>
Cc: Junhao He <hejunhao3@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Leo Yan <leo.yan@linux.dev>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Benjamin Gray <bgray@linux.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Sun Haiyong <sunhaiyong@loongson.cn>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Xu Yang <xu.yang_2@nxp.com>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Veronika Molnarova <vmolnaro@redhat.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-perf-users@vger.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>