rockchip: sdram: Limit usable ram_top to max 4G

U-Boot only works correctly when it uses RAM below the 4G address
boundary on Rockchip SoCs. Limit usable gd->ram_top to max 4G.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
1 file changed