coresight: platform: Use fwnode handle for device search

We match of_node while searching for a device. Make this
more generic in preparation for the ACPI support by using
fwnode_handle.

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>