gpio: Drop sx151x driver

This driver is not used in U-Boot. Drop it and its associated CONFIG
options.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
4 files changed