ARM: dts: berlin2cd: move PMU node from soc to root

Cortex-A9 PMU has no associated memory ranges and "make dtbs W=1" warns
about missing reg or ranges property. To avoid the warning, move the PMU
node out of soc subtree to the root.

Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>