According to ARMv8 architecture reference manual (ARM DDI 0487A.k)
Chapter 'Part H: External debug', the CPU can integrate debug module
and it can support self-hosted debug and external debug. Especially
for supporting self-hosted debug, this means the program can access
the debug module from mmio region; and usually the mmio region is
integrated with coresight.

So add document for binding debug component, includes binding to APB
clock; and also need specify the CPU node which the debug module is
dedicated to specific CPU.
Suggested-by: NMike Leach <mike.leach@linaro.org>
Signed-off-by: NLeo Yan <leo.yan@linaro.org>
Reviewed-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>