coresight: Make sure device uses DT for obsolete compatible check

As we prepare to add support for ACPI bindings, let us make sure we do
the compatible check only if we are sure we are dealing with a DT based
system.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>