coresight: etm4x: Don't use contextID with PID namespaces

As with ETM3x, the ETM4x tracers can trigger trace acquisition based on
contextID value, something that isn't useful when PID namespaces are
enabled.  Indeed the PID value of a process has a different representation
in the kernel and the PID namespace, making the feature confusing and
potentially leaking internal kernel information.

As such simply return an error when the feature is being used from a
PID namespace other than the default one.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Kim Phillips <kim.phillips@arm.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>