ARM: rockchip: Remove the pinctrl request at rk3288-board-spl

If we use the new pinctrl driver, the pinctrl setup will be done
by device probe. Remove the pinctrl setup at rk3288-board-spl.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>