[U-Boot] rockchip: rk3188: add rk_board_late_init() hook

[Philipp Tomsich]

> All other rockchip boards have rk_board_late_init() hook,
> so add it to rk3188 boards also.
> 
> Signed-off-by: Alexander Kochetkov <al.kochet at gmail.com>
> ---
>  arch/arm/mach-rockchip/rk3188-board.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 

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