This patch allows to use the second parameter of gpio
specifier, which is used to specify whether the gpio is
active high or low.

Simply remove specific of_xlate callback() and of_gpio_n_cells
and use default one set by of_gpiochip_add() which allows
to use second parameter gpio specifier.
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>