perf record: Use sw counter only if hw pmu is not detected

perf record: Use sw counter only if hw pmu is not detected

Use cpu-clock-tick sw counter for cpu-cycles only if there is no hw
pmu available. This is the case if the syscall reports ENOENT. In
other cases (e.g. invalid attributes) we don't want the sw counter to
be used.

Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1333643188-26895-5-git-send-email-robert.richter@amd.com
Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>