tegra: Remove tegra_spl_gpio_direction_output declaration from header file

This function is deleted by commit 2fccd2d9
"tegra: Convert tegra GPIO driver to use driver model".

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>