rockchip: rk3308: allow loading larger kernel Image

When compile the curren mainline linux kernel(Linux 5.5-rc3)
with defconfig, the final Image is 29M, it's much
larger than Linux 5.4.

On the current u-boot side on rk3308, the gap between
kernel and fdt is 25M, the fdt will overwrite kernel
Image, so move ftd to a higher memory to give 34M
gab for them.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>