[U-Boot] rockchip: rk3399: spl: remove unused header inclusion

[Philipp Tomsich]

> fdtdec.h is included, but not used in rk3399-board-spl.c: remove the
> '#include'-statement.
> 
> Signed-off-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> ---
> 
>  arch/arm/mach-rockchip/rk3399-board-spl.c | 1 -
>  1 file changed, 1 deletion(-)
> 

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