rockchip: Move pull-up/down enum into a common file

At present this enum is only available to rk3288. Move it so that other
rockchip SoCs can access it. It is needed for the SPL GPIO driver for
rk3999 in a later patch.

Also adjust the enum name to lower case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>