[U-Boot] rockchip: board: evb_rv1108: update README

[Philipp Tomsich]

> After commit d962e5dadc2c("rockchip: mkimage: use spl_boot0 for all Rockchip SoCs"),
> the mkimage will not pad the Tag memroy, so we shoud
> pass a Taged ddr.bin/spl.bin to it.
> 
> Signed-off-by: Andy Yan <andy.yan at rock-chips.com>
> ---
> 
>  board/rockchip/evb_rv1108/README | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 

Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>