Each clock drivers if now fully subclassed, this have the advantage that
we can control the probe order.
Some clocks can have parents from other drivers, for example clocks in the
sun8i_r driver uses clocks from the main clock driver.
This worked before because the sun8i_r node is after the main ccu node in the
dtb and driver are probed in DTB order. This cannot work with the Display
Engine clocks as it is the first node in the DTB.
Tested on: A83T, H5 A64
Tested on: A20 (kevans)
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