We can use GPIOs as binary digits for reading 'strapping' values. Each GPIO
is assigned a single bit and can be set high or low on the circuit board. We
already have a legacy function for reading these values. Add one that
supports driver model.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>