perf kvm: Add pointer to 'perf_kvm_stat' in kvm event

perf kvm: Add pointer to 'perf_kvm_stat' in kvm event

Sometimes, handling kvm events needs to base on global variables, e.g.
when read event counts we need to know the target vcpu ID; the global
variables are stored in structure perf_kvm_stat.

This patch adds add a 'perf_kvm_stat' pointer in kvm event structure,
it is to be used by later refactoring.

Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230315145112.186603-2-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>