sunxi: parameterize H616 DRAM ODT values

While ODT values for same memory type are similar, they are not
necessary the same. Let's parameterize them and make parameter same as
in vendor DRAM settings. That way it will be easy to introduce new board
support.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>