gpio: regmap: Always set gpio_chip get_direction

If you only have reg_dat_base set, then it is input-only; if you only
have reg_set_base set, then it is output-only. Thus, we can always set
gpio_chip get_direction to gpio_regmap_get_direction and return
GPIO_LINE_DIRECTION_IN/GPIO_LINE_DIRECTION_OUT given the respective
register base addresses configuration.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Michael Walle <michael@walle.cc>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>