sunxi: H616: add DRAM type selection

Allwinner H616 SoC supports several types of DRAM memory. To further
integrate other types of memory, we need to add this delimitation.

Signed-off-by: Mikhail Kalashnikov <iuncuim@gmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>