arm64: dts: juno: add missing CoreSight STM component

This patch adds the missing CoreSight STM component definition to the
device tree of all the juno variants(r0,r1,r2)

STM component is connected to different funnels depending on Juno
platform variant.

Reviewed-and-tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mike Leach <mike.leach@linaro.org>
[sudeep.holla@arm.com: minor changelog update and reorganising the STM
	node back into juno-base.dtsi to avoid duplication]
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>