sunxi: Add H616 DRAM support

Allwinner H616 supports many types of DRAM. Most notably it supports
LPDDR4. However, all commercially available boards at this time use
only DDR3, so this commit adds only DDR3 support.

Controller and MBUS are very similar to H6 but PHY is completely
unknown.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Acked-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>