coresight: Introduce generic platform data helper

So far we have hard coded the DT platform parsing code in
every driver. Introduce generic helper to parse the information
provided by the firmware in a platform agnostic manner, in preparation
for the ACPI support.

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>