sunxi: add DRAM support to H6

The Allwinner H6 SoC comes with a set of new DRAM controller+PHY combo.
Both the controller and the PHY seem to be originate from DesignWare,
and are similar to the ones in ZynqMP SoCs.

This commit introduces an initial DRAM driver for H6, which contains
only LPDDR3 support. The currently known SBCs with H6 all come with
LPDDR3 memory, including Pine H64 and several Orange Pi's.

The BSP DRAM initialization code is closed source and violates GPL. Code
in this commit is written by experimenting, referring the code/document
of other users of the IPs (mainly the ZynqMP, as it's the only found PHY
reference) and disassebling the BSP blob.

Thanks for Jernej Skrabec for review and fix some issues in this driver
(including the most critical one which made it to work), and rewrite
some code from register dump!

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>