sunxi: makes an invisible option for H3-like DRAM controllers

sunxi: makes an invisible option for H3-like DRAM controllers

Allwinner SoCs after H3 (e.g. A64, H5, R40, V3s) uses a H3-like
DesignWare DRAM controller, which do not have official free DRAM
initialization code, but can use modified dram_sun8i_h3.c.

Add a invisible option for easier DRAM initialization code reuse.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>