[U-Boot] rockchip: rk3399-puma: reduce env size to 8kiB

[Philipp Tomsich]

> ...even when the environment is saved to SD card.
> 
> With the default of 32kiB, the environment overwrites the SPL
> stage which lives at 16kiB.
> 
> Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher at theobroma-systems.com>
> ---
> 
>  board/theobroma-systems/puma_rk3399/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

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