gpio: pca9570: add slg7xl45106 support

Dialog semiconductors SLG7XL45106 is an 8-bit I2C GPO expander.
The output port is controlled by a data byte with register
address. Add a compatible string for the same. Also update
the driver to write and read from it.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@amd.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>