dmaengine: mv_xor_v2: Fix clock resource by adding a register clock

On the CP110 components which are present on the Armada 7K/8K SoC we need to explicitly enable the clock for the registers. However it is not needed for the AP8xx component, that's why this clock is optional.

With this patch both clock have now a name, but in order to be backward compatible, the name of the first clock is not used. It allows to still use this clock with a device tree using the old binding.