dt-bindings: coresight: Change CPU phandle to required property

Do not assume the affinity to CPU0 if cpu phandle is omitted.
Update the DT binding rules to reflect the same by changing it
to a required property.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/0f7f4105d5ffea6ca4313271f3b3fee69da2106a.1562229018.git.saiprakash.ranjan@codeaurora.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>