sunxi: map DRAM part with 3G size

sunxi: map DRAM part with 3G size

All Allwinner 64-bit SoCs now are known to be able to access 3GiB of
external DRAM, however the size of DRAM part in the MMU translation
table is still 2GiB.

Change the size of DRAM part in MMU table to 3GiB.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>