sunxi: h6/h616: Reuse common DRAM infrastructure

sunxi: h6/h616: Reuse common DRAM infrastructure

H616 rank and size detection code is superior to the H6. Nevertheless,
they are structurally the same. Split functions from H616 into new file
and reuse them in H6 DRAM driver too. This should also fix some bugs for
H6 too, like incorrect DRAM size detection.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
[Andre: back out panic if test fails to allow 2^11 columns]
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>