perf evlist: Add helper to check if attr.exclude_kernel is set in all evsels

perf evlist: Add helper to check if attr.exclude_kernel is set in all evsels

The warning about kptr_restrict needs to be emitted only when it is set
and we ask for kernel space samples, so add a helper to help with that.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-fh7drty6yljei9gxxzer6eup@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>