FROMLIST: dts: bindings: Document device tree bindings for Arm TRBE

Document the device tree bindings for Trace Buffer Extension (TRBE).

Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Link: TODO ADD LINK TO V4 WHEN POSTED
Change-Id: I55b1f0985331a41d1811f40c795fb61d42872e2a