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 <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>