sunxi: A64: use H3 DRAM initialization code for A64 as well

The A64 DRAM controller is very similar to the H3 one,
so the code can be reused with some small changes.
This refactoring does not change the code size for the existing H3 part.

[Andre: rework from #ifdefs to using socid parameters in static
        functions, minor fixes, merging in fixes from Jens]

Signed-off-by: Jens Kuske <jenskuske@gmail.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>