coresight: Support for ACPI bindings

Add support for parsing the ACPI platform description
for CoreSight. The connections are encoded in a DSD graph
property with CoreSight specific variation of the property.

The ETMs are listed as the children device of the respective
CPU.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
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>