pinctrl: meson: fix gxl ao pull register bits

AO pull register definition is inverted between pull (up/down) and
pull enable. Fixing this allows to properly apply bias setting
through pinconf

Fixes: 0f15f500

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