ARM64: dts: marvell: armada-cp110: Add registers clock for the PCIe nodes

This extra clock is needed to access the registers of the PCIe host
controller used on CP110 component of the Armada 7K/8K SoCs.

This follow the changes already made in the binding documentation (as
well as in the driver): "PCI: armada8k: Fix clock resource by adding
a register clock"

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>