sunxi: clock: H6: add A523 CPU PLL support

sunxi: clock: H6: add A523 CPU PLL support

The Allwinner A523 features 8 CPU cores, organised in two clusters, both
driven by separate PLLs. Also there is the DSU PLL, which clocks the
hardware that connects the cores to the rest of the system.
And while the PLL registers itself are very similar, they are located in
a separate register frame, outside the main CCU, and also the register
controlling the CPU clock source (mux) is different.

Provide a separate function that reparents the two clusters and the DSU,
while their PLLs are programmed. For the actual PLL programming, we rely
on the existing shared routine.

The selection between the new A523 routine and the existing code is made
with C if statements, but since the choice is effectively made at compile
time already, the compiler optimises away the other code paths, leaving
just the one required function in.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>