arm: dts: vexpress: add missing CCI PMU device node to TC2

The CCI device node was added to vexpress CA15_A7(i.e. TC2) much before
the CCI PMU support and binding was added. This patch adds the missing
PMU node so that CCI PMUs can be used on TC2.

Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>