pinctrl: meson-gxl: Add missing GPIODV_18 pin entry

GPIODV_18 entry was missing in the original driver push.

Fixes: 0f15f500 ("pinctrl: meson: Add GXL pinctrl definitions")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>